Smartphone with multiple concurrent bluetooth connections

[Stewrat]

I'm looking for a smartphone to use in-car as satnav and hands-free phone.

Doing some research, it seems this isn't necessarily straightforward - mainly as the smartphone has to be able to support multiple concurrent bluetooth connections to make it work.

It's absolutely critical that the navigation continues to work if I take a call, but this feature (or lack of) doesn't seem to be listed in the specs most of the time.

So ...

Can anyone recommend a combo that will work?

Smartphone - must have decent PDA functions, ideally Windows Mobile but not essential.
SatNav - probably TomTom but not essential.
Phone headset.

Thanks for any tips or pointers.

Stewart