I'm using Minicom (serial port software for Linux) for interacting with my GSM modem. Actually now I'm trying to use one of my mobile-provider's services with AT commands.
Here I say, I want to see my balance:
AT+CUSD=1,*555*87*1234#
OK
+CUSD: 1,"this service will deduct you 5cent from your balance, to continue please enter 1",15
So, here I sent "1", but nothing happened and the session got closed.
AT+CUSD=1,1
OK
Nothing happened, but the session closed.
With a normal phone, after entering 1, I will get my current balance.
Answer
The format of the command is AT+CUSD=[<n>[,<str>[,<dcs>]]], and the second parameter, <str>, is a string that should be enclosed in double quotes. E.g.
AT+CUSD=1,"*555*87*1234#"
AT+CUSD=1,"1"
See 27.007 for more details about AT+CUSD and V.250 for general AT command handling.
If your phone gives an OK response to AT+CUSD=1,1 that is really bad, it should have given ERROR. V.250 is crystal clear on this:
String constants shall be bounded at the beginning and end by the double-quote character