If you need to go back to Verizon, I don't think you will have a problem.
About 3 days after I switched from Verizon to ATT, a Verizon rep called me and offered me some things to make me come back.
1. I could bring my number back to Verizon, and they would take care of all switching for me.
2. As an incentive to return to Verizon, she offered me 2 free phones (for my 2 family share accounts)
3. Then she offered me a couple of free months of Verizon service if I would come back.
She wanted to know why I switched after 10 years with Verizon. She wanted to know why I switched to ATT. One word iPhone. She tried to convince me that Verizon's phone was better, but I told her that I had been to the store and tried it for myself. She said that it sounded like my mind was made up and nothing would make me come back to Verizon. I said, not until an iPhone works on the Verizon network. She thanked me for my time.
I have been an AT&T customer ever since. I bought a Sony Ericson W580i as an interim phone until the 3G iPhone was released.
I called AT&T customer service yesterday and was told that there would be no problem switching to an iPhone. I have only had my AT&T account for 3 months. No ELIGIBILITY PROBLEMS.
She said that there was only the sales price $199 for the 8 GB and $299 for the 16 GB. There is no subsidy for anyone at this time. $199/$299 is the full price of the phone for new customers or upgrades. There is no problem for everyone to update to the iphone, regardless of eligibility. The price is the price for everyone.
I know this is contrary to what I have read on here, but this is from AT&T's customer service phone line as of June 26. I asked specifically and several times, but she was adamant that there would be no problems at all with me getting an iPhone.
She also told me that if my primary phone line was the iphone, no corporate discounts will apply. If my primary line was not an iphone, I could keep the corporate discount I currently qualify for. She switched my second line to be the primary line in preparation for buying an iphone. My iphone will be charged at the rate for a second phone on a family plan. I will still have to pay for the iphone internet package of 200 text messages and unlimited internet.
I hope you can get AT&T reception well enough for an iPhone.