I used a 3G(WCDMA) mobile data modern, which dail up in embedded linux, sometimes I find the USIM card is out of balance, so it can't dialup normal, I just search the modern manual to find the AT command can be help.
I use command called "SYSINFO", but it doesn't work. whether or not it have a method to judge the USIM status which is out of ballanace.