I posted this on someone elses thread a few months back. Read it, its long but I know what I am talkin about lol.
Verizon is by FAR the most reliable. I could type for 4 hours about all the pros and cons about most main carriers (just cuz I do alot and i mean A LOT of reasearch about all the different types of technology invloved.) I will keep this quick to try to help you out.
Verizon and sprint use CDMA (no sim cards). TMobile and ATT use GSM (sim cards)
As long as you stay in the US mainly, CDMA is the way to go. Here is why:
-CDMA signals travel farther and penetrate buildings much better
-CDMA towers hold much more bandwidth than GSM towers (if you have ever been to the Kentucky Derby or the Inauguration or any place with THOUSANDS OF PEOPLE in one spot, people using GSM may have difficulty making/receiving calls for this very reason)
-CDMA users generally have no problem making/receiving calls when they only have one "bar". In my experience with ATT and Tmobile, when you only have one "bar", the call is choppy.
Besides those reasons, I recommend Verizon because their network just covers more of the US than anyone elses. They are the largest network in the US, and they offer discounts for damn near everything. They offer insurance on ALL of their phones, and you also can specify 5 numbers (10 for family plans) that are not on Verizons network that you can call for free whenever. If you choose NOT to get a Smartphone or Blackberry, you can get unlimited internet for only 15 bucks a month. Cheaper than most i think. I have the Blackberry Storm and love it. The REQUIRED data package is $30 a month.
All in all, in major cities, you shouldn't have real trouble with any provider, but i know verizon would shine once you go deep in hospitals, basements, elevators, ect. Plus in all the places I have traveled, I have had service, and I cant tell you how many times I have lent my phone to someone to use a call WHILE WE ARE ON A HIGHWAY. That makes no sense to me. Once in Chicago, my buddies Tmoble phone lost service in the mall with the lego place lol. (on the freakin magnificent mile)
Last note, Verizon offers you 30 days to completely try them out. If you aren't happy, take the phone back and walk away. I am 90% sure no other place offers this, but Verizon does because they have the lowest drop rate (which means fewer people leave verizon than any other wireless company).
As for my cell phone, I have a Blackberry Storm, but I used to have the Gzone Boulder. Its the waterproof one they offer. Flippin sweeeet.
Good luck man, I tried to keep this short lol. If you have any more questions, jus shoot me a message. I know damn near everything to know about how these things work.