In some cases you may receive a CMS Error 500 error message from your modem. This error message indicates, that for some reason the modem was not able to deliver the message. This error can happen if:
The phone number you try to send your message to is invalid
There is no network coverage
You don't have enough money on a prepaid subscription
The short message service center of the GSM network operator is temporarily out of service
The GSM cell is overloaded
