problem with communicating with the GSM modem

hi every one My Objective: i am trying to test my new GSM and GPRS modem that i brought from local electronics market. And i want check the functionality like sending and receiving SMS,CALLING,GPRS functionlity etc..

for this i am trying to test this modem using AT commands... these are the results that i am getting

RDY

+CFUN: 1

+CPIN: READY

Call Ready
AT
OK
AT+CMGS="78XXXXXXXX"
> HAI I AM WORKING....
>
+CMS ERROR: 302

this error message i am getting when i am pressing "ctrl+z" to end the message. And this Error : 302 is indicating that "Operation not allowed" the simcard that i am using is postpaid ....

and some times i also getting the following results

RDY

+CFUN: 1

+CPIN: READY

Call Ready

+CPIN: NOT READY

which is indicating that sim card is not detected...

can any one who is reading this post help me out..

thanks in advacne

Hi every one for the fowwing error message

RDY

+CFUN: 1

+CPIN: READY

Call Ready

+CPIN: NOT READY

i found that when ever i powered on my Modem that voltage at the pins of the simcard reader is around 2.57V and after some time it is becoming 0V then i am getting the

+CPIN: NOT READY

message

-> why the voltage becoming 0V after some time???? -> how to solve this problem???

anyone who is reading this post please help me out.. thanks in advance...