GSM Shield Problem...

I am having a problem with my Geeetech GSM shield, which I am connecting to an Arduino Uno. I am trying to use it to send a text message but every time I try executing the code, the text message is sent once ans then stops sending because the SIM card I am using breaks down in the sense that it stops sending text messages even on a regular phone (it continues to receive messages and calls, though). Has anyone encountered problems such as this one? Any advice would be greatly appreciated!!

Once the SIM is in this stte, can you make outgoing calls when it's in a regular phone? If so, I wonder is your cell phone provider is noticing that it sent a text from a weird device and has flagged it as a spammer or something....

Hi Mr. Jon-White,
What do you mean by stte? I can still make outgoing call when it is on a regular phone. The GSM shield acts as a phone. It has a SIM card in it that sends a text message to another phone. On the receiving phone, the text message looks like it comes from a phone because it displays a phone number. Can you please explain what you mean by my cell phone provider flagging the number as a spammer? I don’t quite understand. Thank you so much!!