Pause the game, then access the cell phone. Select "Dial", then enter one of the following numbers, and choose "Call" to call the corresponding service:
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Service --> Phone number

Airport --> 5553597

Big Willy's Cab --> 8198415

Bling Bling --> 5554233

Brown Baggers --> 5553765

Cocks --> 5552626

Company of Gyros --> 5554976

Cycles --> 5552453

EagleLine Yellow --> 180174

Emergency --> 911

Eye for an Eye (Zombie Carlos) --> 5555966

Foreign Power --> 5552046

Forgive and Forget --> 5554448

Freckle Bitch's --> 5556328

Friendly Fire --> 5554867

Fire Department --> 5553473

Giftshop --> 5557577

HazMat --> 5556677

Image as Designed --> 5558459

Impression --> 5553248

Leather and Lace --> 5552662

Legal Lee's --> 5559467

On The Rag --> 5555926

On Thin Ice --> 5552564

Police --> 5557973

Pimps 'R Us --> 5557467

Rim Jobs --> 5553493

Rusty's Needle --> 5558287

Ship It --> 5557447

Spelunkers --> 5552283

Suicide Hotline --> 4876837

Tee'N'Ay --> 5559866

TNA Taxis --> 4558008

Ultor Security --> 411