Just look online for an LG model you think is close to what you had and buy one that was built / configured for the AT&T network. Should be no problem to switch over to it online or at the AT&T store. Ebay or amazon is a good source to buy the phone - NOT AT&T. I do this all the time on Verizon when a phone craps out - just buy what I like for $50 (refurb or even new) on Ebay and sign it up online at Verizon. I still have an original RAZR V3 running on the family plan!
Don't give in to this smartphone BS. Too much $.
G