Which cell phone carrier has the best coverage at Camp Dwyer in Afghanistan?

[annabanana1]

I need to know which American cell phone carrier has the best coverage in the Camp Dwyer area in Afghanistan. This area is in South Afghanistan in Helmand Province. I have checked several global coverage maps for tmobile, ATT, and Verizon, but I can't tell who has the best coverage over Camp Dwyer. Has someone been to Camp Dwyer who can tell me from experience what carrier has the best coverage? Thank you!
I should not have used the term "coverage." Technically it is global roaming.

 

[allkhuffasch]

I haven't to military bases or camps but THERE'S NO COVERAGE IN MILITARY CAMPS IN AFGHANISTAN (i have a friend in Bagram working as a computer operator)