If AT&T's network will still be compatible with it in 2017, I will definitely rock my iPhone 2G on June 29, 2017 to mark the 10 year anniversary of it's release. As of this day, it's still completely functional with good battery life and still activates when you put a SIM card in, although I have to use an adapter. Hopefully it stays that way for roughly another 2 years. I'm sure the phone will still work, it's the network I'm concerned about.
GSM will be around for a while to come. UMTS will likely perish before GSM does.