2.5G iPhone an iPod after pulling old sim

After pulling the old sim out of the 2G phone and popping it into the
new 3G phone the old iPhone acts like it always did except it can not
make phone calls. It is not bricked or any thing.

It acts like a super i Pod Touch.

I put the unactivated sim that came with the new 3G phone in the old
phone to keep it safe in case someone wants to activate it on AT&T in
the future. Trying to make a phone call momentarily locks up the old
iPhone.