My Ericsson T39m can synchronise the calendar and phone book over Bluetooth (and possibly infra-red) with anything that speaks the standard Bluetooth PIM profile. The HTC Desire can't do that.
The Ericsson T39m can exchange calendar and phone book entires over Bluetooth and infra-red with anything that speaks the standard OBEX profiles. The HTC can receive phone book entries (but prompts for every single one, making it impractical to do a bulk transfer), but cannot receive calendar entries. I'm not sure if it can send entries either - I didn't investigate that.
New phones are supposed to be better than old ones, not worse!