Can I put my sim card from my lg phone into a hammy down 3G iPhone?

Without having a data plan? Can I do this and just use it as a phone?

Added (1). I have AT&T

Yes you can only if the SIM card is the right size (mini-sim). The iPhone will still work as a normal phone just it won't have 3G.

Nope.AT&T will apply a data plan once it is in the iPhone.

Oh & its 'hand me down'

No.AT&T will get notification that you did so and add a data plan after a certain amount of use. I used to work for them and know how they work. You will have to add data. However, the cheapest is 15$ which gives you a lot of web usage and isn't that bad of a plan. If you don't want data at all, I'd advise against using the iPhone. The iPhone 3G doesn't use a micro-sim, so if you have a micro card you'll have to go in-store and get a full size card.