I have my att sim card from my old phone and want to switch to an old t-mobile sidekick i says needs sim code?

The reason its probably asking for a special sim code is because it doesn't recognized the sim card. T-mobile and ATT are notorious for "locking" their phone, which is to say not allowing ots use with any other sim card except their own. One of the only ways to get the T-mobile phone to work with the ATT sim card is to unlock it.

T-Mobile sidekick is locked to be used phone only under T-Mobile the phone would need to be unlocked to use att sim however T-Mobile does not provide unlock code for the sidekick

You need to look up online how to unlock the sidekick for other sim cards. T-mobile will tell you it cant be done but it can because my friend bought an unlocked sidekick off E-Bay and put his AT&T sim card in it and it works fine.

The code you are looking for is called a subsidy lock code and you have to get it from Tmobile, the company that marketed the phone in the first place. You can also go to cell-unlock.com and pay to get the phone unlocked then you can use it on AT&T

you have to get the sidekick unlocked because its ur att sim card is not gonna work on a tmobile phone. Two different service providers...

you need to unlock it. There are ways to get around it, but its complicated like saying you have to travel to mexico and stuff. i add att and my sim card does not work in my sidekick phone....i had to get a t-mobile sim card

The phone is prob locked to worth with t-t mobile sims Only

You need a sim card from T-mobile, for a T-mobile phone.

the phone is locked into t-mobile service...either you need to get an unlocked or an att phone or switch to t-mobile..

also there are places that you can pay like $20 to unlock your phone for you.

contact att by their help chat or by phone