I'd really like to get an iPhone 5 this fall but I need to learn some things first.

I have 1 rule. I will not get stuck in a contract ever again (never has it not caused me great grief) and will only do month to month.

My plan initially was to go buy an iPhone 5 straight from Apple and just take it to a service like Tmobile or Verizon and say give me service please. Apparently it isn't that easy. Verizon told me if I buy a phone from Apple it will have to be the 'Verizon' version of the iPhone. Are they not all the same as far as hardware? What do they mean by this? Does that mean if I buy a 'Verizon' iPhone from apple I am always and forever stuck with using Verizon and no other service, even though I payed full price for the phone? Why? What if I'm not happy with Verizon and want to take my iPhone 5 to another service at some point?

What makes a 'Verizon' iPhone a Verizon iPhone? Why can't I pay full price from Apple, get it activated at Verizon and use their service for however long, and then next year decide to go with Tmobile? Remember this is all assuming I find month to month plans which I can quit anytime I want. I just don't understand WHY if I pay 6-800 dollars for a phone that I don't have a choice of who's service to use.