I'm comparing the available items too. The current options I see are:
Xlink BT - supports 3 cell phones
Xlink BTTN - supports 3 cell phones + a land line
Cell2Tel - supports 2 cell phones + land line
GE Bluetooth Cell Fusion Gateway - 2 cell phones
My two main requirements are:
1) pairs and stays paired properly
2) able to dial out normally without any wacky button sequence
#1 is likely a crapshoot as my limited experience with Bluetooth in general is that it can be flaky. My Pre pairs nicely with my Pioneer AVIC-D3 in my car for voice calls but doesn't work at all for any music playing.
Both Xlink boxes and the Cell2tel satisfy #2 according to the manual. They do give options to choose a different phone to dial out from but they default to land line, then cell1, then cell2. You can enter a code to manually override this which is fine. The GE Bluetooth one ALWAYS requires you to dial #1# or #2# to call out which is unacceptable to me even though this costs 1/3 of the others.
I'm going to buy the Xlink BTTN which is about $100 on amazon, I'll report back as to how it works. If it goes well I will be ditching my land line. This one does keep the flexibility to integrate it with some type of VOIP service since you can feed it a phone line so I could possibly set up that if I'm not satisfied with making all outbound calls with a cellphone.