I have jailbroken and unlocked my 3gs 4.2.1 (8C148a) and it was doing fine and working with t-mobile. I had to do a restore and now when i put in my tmobile sim it says different sim detected. The crazy thing is i can still recieve calls but after the call it goes back to the iTunes restore screen. I am running the ipad baseband. I took a look at this http://www.hackint0sh.org/f236/155233.htm but cannot use it because it stops at 4.0.1. Any help will be appreciated thanks in advance.

You need to hacktivate your phone.
First run greenpois0n rc6.1 to jailbreak
Run redsn0w 0.9.6rc8 and select only "install cydia" - this hacktivates
finally install ultrasn0w.

OR

if you have a mac, use pwnagetool 4.2 to make a custom IPSW, then install ultrasn0w to unlock.

This is no new or special problem, but it does highlight that you need to be extremely careful when you restore or upgrade your phone.

OH yes that worked! Thank you so much