I just found a strange feature of most mobiles – a Message Validity setting. This is the time an SMS message will try to be sent before it is killed off if it is not delivered. Some phones you can set this for something like 5 minutes as a minimum. General you would set this for something like a week. My phone had this set for 24 hours which is probably a bit short. If the phone it is being sent to is switched off for 24 hours it will never get through. I never knew this until today.

I have just done some searching, and the paramaters of note are VP and TP. TP is the retry time, and VP is the maximum retry times. The values for VP with the SonyEricsson modem are 0-255. With an algorithm meaning from 5 minutes to 64 weeks…. Rather Interesting