Trouble with phone (by 2 users)

I have exact same problem. new phone for my daughter. she created a password and either she cant remember the right code or its locked up. Same problem w/att not providing much help. It tells me to enter my device password (if thats the one she cant remember, I guess thats problem). It also has put me on a timer cuz my daughter tried to input the password too many times. I read that replacing the sim card is a possible help if you run out of possibilities. It that true? can anyone help. Ive been paying on this phone for last 2 months w/o being able to use phone. nearest store is over hour away. pls help, thx jaci