No, when you switch from AT&T to Verizon, you will have a different contract with a different mobile cell phone service provider. Their pricing for their plans will be similar, but Verizon offers more in their 'middle tier' data package than AT&T does, plus Verizon has better coverage in rural areas. Those two things together are very strong selling points for Verizon. Also, Verizon is gearing up to have a nationwide LTE/4G network sometime in the next 2-3 years. AT&T hasn't even made an attempt to go to a 4G network outside of trying to out right buy the Sprint network. However, the FCC denied AT&T's request to make the purchase. Now that Verizon has got the iPhone, along with good coverage in their service areas - Verizon is surely to come out on top as America's leading mobile cell phone service provider.
As for your sister's AT&T bills, she should check her mail more carefully, the bill may not be obviously marked, or it is being over looked in a pile of junk mail. She should try to set up her account to where she can pay directly from her phone. When the bill is due, she dials a specific number, punches in her code, then viola, the bill is paid by an electronic transaction from her bank account. I have several friends who are still with AT&T, and they pay their bills this way. They are sent a reminder text that their bill is due, then they just pay it immediately. Far as I know, none of them have been charged any late fees.
If your in a rural area, I would get away from AT&T as soon as my contract is up. Go with Verizon, especially since CDMA is more widely used in the USA.
