Secret Service

Here is a list of all phones and their locations, you can check which ones you have already gotten by going to menu, cell phone messages and it will give you the names of the phones by map that you have picked up:

Inaugural Assault (7 Phones)
P1. [Adios] This is located northeast of the Lincoln Memorial almost between two pillars.
P2. [I Am El Arma] This cell phone may require a little bit of searching. It is dropped by one of the terrorists in the battle at the beginning of the stage. So it's in open area where the helicopter crashes.
(Be advised that you cannot back track to this location when you move onto the next area, fire will be blocking you from returning. You will come back to this point later in the level so there is no need to restart the level.)
P3. [All Assaults Green] In the area where you have to snipe the two RPG gunners. Kill a man with a hoodie and he will drop it.
P4. [Delgado DUI] After (it was before on my play) killing the RPG gunner on top of the Lincoln Memorial (4th gunner), three enemies will attack you as you move north. One of them will have the cell phone. He is wearing an orange vest.
(Be advised that once you start to go north of the Lincoln Memorial in a narrow walkway, a fire will block your path from returning to the earlier part of the level until you kill the RPG gunner at the LCD screen.)
P5. [Reacquire Targets] After passing through a narrow path, you will see a bunch of stacked red boxes. There is a dead SS agent leaning on a metal fence. Northwest of him is a tent. Inside the tent there is a control panel, the cell phone is on top of it.
P6. [Canisters] After killing the 5th RPG gunner, follow the path until you begin moving east again. There will be four portable toilets in the vicinity and a trailer on your left when you are facing east. Enemy will attack in this narrow area. One of them has the cell phone.
P7. [Earn Every Penny] When you return to the Lincoln Memorial, there will be four terrorists in a gunfight with the rest of the SS agents. One of them has the cell phone. If you can, search their body after you have killed one of them. Once you have killed all of them, the level will end quickly. So you must rush to the cell phone and pick it up. If you miss it, you have to restart the level.

Coup D'etat (4 Phones)
P1. [Target Number Two] At the beginning of the level you will get a prompt to press LB to throw a grenade. You will encounter enemy here. Once they are taken care of, the first room on the left is a small office. The cell phone is on top of the desk.
P2. [Reservations] After hacking the door open, you will be attacked by three men. One of these has a cell phone.
P3. [Building's wired] In the room northeast of the bomb you have to diffuse. The room is green. The cell phone is on a bench.
P4. [Vargas's Speech] After diffusing the bomb you will come to a large room with a T shaped stair case. You will be attacked by enemy soldiers here. One of them has the cell phone.

Filibuster (6 Phones)
P1. [Lost Control] In the hallway with the three fire extinguishers, you'll come into contact with an enemy that is carrying the cell phone.
P2. [Inner Circle] After you diffuse the first bomb, follow the wires until it goes into a wall. Now face south and you will see the cell phone sitting on the pedestal of the bust. There is a grenade on the ground to the left.
P3. [Not the Senate Chambers] When you come to a long set of fancy stairs, you will be attacked by three men. One of them has the cell phone.
P4. [For Guadalupe] In the circular room where you get ambushed by guys on the ground floor and from guys above. Kill one of the guys with the shotgun. He's usually on the left side.
P5. [Explosives Discovered] In the same room as #4. It is on a bench to the southwest.
P6. [Past, Present or Future] When you drop down in a circular room, one of the terrorists here has it.

Urban Legend (5 Phones)
P1. [Diplomacy of Death] After going down the elevator and arguing with your superior. You will come to a tunnel with a rail car. In this tunnel, east of the rail car is a control room. The room to the south east of this has a small control panel in the middle of the room. The cell phone is on top of this control panel.
P2. [Wichita] Follow the rail/track until you get to an electric fence. you can go either left or right. Go right and you will reach a room with a few boxes and enemies. There will be two men on a slightly higher level on the north side of this room. There are also two double doors here. You can reach this by jumping on the boxes. One of the guys you killed had a cell phone.
P3. [Garfield] After the last cell phone, move to the next room to the south. Clear the enemies and go up onto the catwalk. You will see it to your north once you get onto the catwalk.
P4. [Who Are They Talking To?] After tripping the laser which closes the door, you will be back in the tunnel with the rail cars. As you move southwest along the tunnel, there will be a room on your right. When you enter this room, the cell phone will be on the left side.
P5. [Invaded by Costa Sentava] You will reach a point where there are 4 turret cameras (C2-C5) and you have to hack a computer to open the electric gate. After opening the gate, you will see it on top of some boxes as you pass through the gate.

Collateral Damage (2 Phones)
P1. [Pinned Down] this phone is dropped in the darkened room after you kill the enemy.
P2. [Black and White Politics] after the 3rd terminal, go through the tripwire beam rooms and you will end up in the Missile Silo room. Go down the second set of stairs and the phone is on the corner of the platform.

Rogue Agent (4 Phones)
P1. [The Smell of Conspiracy] after you taser the open room of agents, go up the stairs and the phone is sitting on top of the desk in the northwest corner room.
P2. [Shut Him Up] after the checkpoint, you will enter a room with four turret cameras. The phone is sitting on top of a tarp covered crate at the base of the far stairs hugging the wall.
P3. [Bead on Pierce] after you clear the turret and tripwire beams in the tunnel, you will be engaged by agents. You will be in the train depot chamber. One of the agents you taser will drop the phone.
P4. [Embassy on Fire] after returning to the train depot chamber once you re-power the grid, you will go in a tunnel with many agents. One will drop the phone when tasered. It’s right before the staircase with all the white house signs.

Habeas Corpus (7 Phones)
P1. [White House Tour] as soon as you go up the stairs, you will taser an agent and he will drop the phone.
P2. [Poet] upstairs, you will come to a room with a bust statue in the centre of the room. Clear the agents and go right into the next area. Turn right into the first room. Once inside, you will get ambushed by two agents. Once they are tasered, one agent will drop the phone.
P3. [Veep Terrorist] at the top of the stairs (dual entry), there is a door to be hacked. Once inside the room, there is a cell phone sitting on a dresser.
P4. [Nameless Assassin] agents will blow a door down. Taser all the agents. One drops the phone.
P5. [New Sentava] after clearing area with number 4 above, go up staircase and finally go down a series of steps. You will enter a dark room. Taser all guards and one will drop the phone
P6. [Number One Observatory Circle] when you checkpoint that ask you to assist in the assault on the oval office, look for door in the hall with a keypad. Once inside the room, the phone is laying on a desk.
P7. [CVX shipment] found on one of the enemies storming the oval office after you kill him.

Last Stand (4 Phones)
P1. [Package was Delivered] laying in the rose garden. I am not sure if it fell of an enemy after he was shot, but after you clear the area, search the ground near the centre.
P2. [Secure Meetings] on the floor right next to the TCW .308.
P3. [Media Blackout] after clearing the enemies from the roof as a sniper, rejoin the agents. Once the fire fight ensues, turn around and phone will be on a shelf in the oval room.
P4. [Educate Him] after clearing all the enemies from the sniper post, you are called back to the oval office. When you cross the rose garden, there is a guy lying in the middle of the garden. The phone is near him.

Extraction (5 Phones)
P1. [Gas] After you clear the pool area, POTUS goes inside the pool building. The phone is on the ground around the empty swimming pool. It was dropped by one of the enemies you killed.
P2. [For Our Family] in the next area, you will be ambushed by enemies near a large tree. One will drop the phone when he is killed.
P3. [Payday] in the next area, on the ground near a dead agent. He is up against a wood table with three wooden chairs.
P4. [Presumed Dead] you will pass under a wooden walking bridge. Clear the enemies. One drops phone near the large vine covered gazebo.
P5. [Beach House] right next to number four, before you cross the bridge, it is behind the hedges next to a dead agent.

Expatriate (6 Phones)
P1. [Throwing Down Their Arms] after you enter a briefing room with the large white dry erase board in front of you, turn right and go around corner. The phone is on the floor near a dead agent.
P2. [Bail Out] you will clear two rooms with blue carpet. When you exit, the phone is on the floor behind the seats you are facing.
P3. [To All my Agents] after you cross in the “B area”, you are ambushed by a lot of enemies. One enemy drops the phone when killed.
P4. [Agent Foster] after you find the alternate route, go up the stairs. An IED will explode. Kill all the enemies and retrieve the phone from the ground after it is dropped.
P5. [Coming Home] turn right at the top of the stairs. Kill the guy at the end of the hall. To the right, you will see an enemy at the base of the stairs. Kill him and he will drop the phone.
P6. [Our Mission] after retrieving the freeze spray, work your way through the plane. Right after the checkpoint, shoot the guy at the top of the stairs and he will drop the final phone.

Please note that if you pickup and phone and die or restart, you MUST pickup the phone again.

Thanks to Rocha12
http://www.xbox360achievements.org/forum/showthread.php?t=16...