Hi G-prime,
I have exactly the same problem (Jabra BT250 and 800MHz PBTi). After doing some search on apple's support i found out that only the D-Link DBT-120 bluetooth adapter would support headsets on a mac.
Bought the damn thing, installed it, still didn't work: "your hardware doesn't support headsets over bluetooth".
Did a bit more search, found out that a bluetooth firmware update was needed. Downloaded it, installed it. Still doesn't work!!! 😡
Did you have any better luck?