I had asked this question before:

Apart from the timed syncronization, would it not be good if
syncronization takes place only when new mail or any changes take place
on either the groupwise or phone ? Other than keep on sychronizing on
intervals even when nothing new has happened ?

The answer I got was YES: If sms is enabled.

But does this mean I will recieve an sms first, then I will do the
synchronization manaully or the palm gets the sms and the it synchronizes
the mails automatically
Or does it send me an sms after it does the synchronization automatically