iPhone 3g sim work in iPhone 2g?

[fleali88]

well I found a simpler solution, I jailbroke and activated the 2g iPhone , loaded bootnueter and flashed the baseband(very easy). Now I can put my iPhone 3g sim in it when ever I want and no changes are made with billing, the2g also accepts tmobile sim cards now too.everything works on both phones when the sim card is in. It's awesome.it's now literally plug and play.

thats what you do lol

 

[richxps]

hate to fire this thread up again but i put my 3g sim in my old iphone and it did downgrade my data plan, now i put my sim back in my 3g iphone the data plan stayed the same 20 dollar plan. Now can i just use that plan on my 3g with out any additional charges ? or should i call ATT and have them put me back on the 3G data plan ?

Now to avoid this , would unlocking the 2G iphone solve this ? im looking to switch between iphones from time to time and want to avoid this data plan change issue.