Can anyone lay out the SMS Sync process for me?

We are using SMS to keep our mobile devices in sync /w Groupwise and it
works wonderfully (GWMobile 2.02, GW 7.02).

The question pertains to the fact that users are seeing like 300 SMS
messages a month on their provider's bill.

I know the actual Groupwise messages are sent via SMTP. So my question-
what is actually happening during the SMS synchronization piece?

Thanks in advance!