This situation can have been seen on the Siemens TC35i running version 03.01

You must reset the software in the GSM terminal.
 
Stop the subsystem using option 18 on the SMS menu or command ENDSMSSBS.
 
Use the following sequence of AT commands to reset the terminal. (You can use STRITF from your 5250 panel or connect the GSM terminal to your PC)
 
 
ati <enter>                                            (Determines the version )
       SIEMENS
       TC35i
       REVISION 03.01
 
       OK
 
at+cpms="MT","MT","MT" <enter>        (Prepare to reset the memory)
 
        +CPMS: 0,25,0,25,0,25
 
       OK
 
at+cpms="SM","SM","SM" <enter>        (Resets the memory)
 
       +CPMS: 0,50,0,50,0,50
 
       OK
 
at^smso <enter>                                  (Power off)
 
       ^SMSO: MS OFF
 
       OK
 
Make sure the Siemens T35 is connected to you iSeries and the power is ON.
Restart the subsystem us option 17 on the SMS menu or command STRSMSSBS.