maybe a problem with his settings on the bb/phone?
while on a call, data will not go through. once the call ends, data should flow through (although if you are using data and you get a call and there is no continous data traffic at the time of the incoming call, the data session should be interrupted).
this should change with next gen voice/data service that can support simultaneous voice/data traffic.
gsm service is assumed (since you said it is a 6280), not 100% sure how cdma voice/data is treated, although i think it is similar.