I have a client who has to turn the wireless function "off" then back "on" again to force the replication. Any thoughts on why?

Are you on BIS or BES?
On BES, i find reconcile now will force the BB to synch

Is turning the radio on/off is own idea?

to my understanding its the only way email will be forced to the unit any idea as to why?

well i guess when you turn the radio off and then on again, the handheld makes a fresh connection to the provider/server and so new emails will be pushed through...

but emails are pushed through immediatly with BES, and with BIS arent they forwarded straight away?
(my knowledge on BIS is limited)