Lumia 900 cannot get to unlock screen to enter code

[pickles1968]

I have a lumia 900 locked to At&t. I put in an inactive sim from straight talk. The phone fails to bring up unlock screen to enter code. I have tried the numbers on dial pad also. Does the sim need to be active? Or, is there another way to reach the unlock screen? Please help. Thanks

 

[Laura Knotek]

Do you have an AT&T or T-Mobile SIM from Straight Talk? If it's an AT&T Straight Talk SIM, you won't need to unlock the device.

 

[pickles1968]

I had a straight talk card in it, but my wifi wouldnt work, also, couldnt text half my contacts. Odd. I have tried keypad entry #7728.. to no avail? I am wondering if there is another keypad entry to force unlock screen? Is an att locked phone, and had an active straight talk sim in it. any help would be greatly appreciated.