Speaking about the tablet as a phone, would it suffice to make it behave as a bluetooth headset of your bluetooth enabled phone ?
Now that we have Bluetooth 2.0 and A2DP (or ADP?) the bandwidth should suffice for both connections, shouldn't it ?

And as we are at it, why not sync the contacts with the Contacts app in the tablet.
And also improve the "Internet Call" module with a "Phone Call" option where I can either type the number to call or choose the contact to call and let the phone handle it while using the tablet as bluetooth headset (thus using its speakers or its headphones).

I think that would be more than enough to make everyone happy. Me at least.
The phone is another device, the phone is hidden in my jacket and has its own battery. I can bring only my phone with me and leave the tablet at home.
While browsing the web on my tablet (via the phone connection or WiFi) and recevie a call, I will be prompted to answer it ON THE TABLET.
Same for SMSes.

This already happens on the Mac if you have a good bluetooth phone, like my very old Ericsson t39m (the first bluetooth phone!).
Pairing it with the Mac and using the Addressbook application I was able to make/receive calls from the Mac, reading and sending SMSes THRU the Mac.

Why it can't be done on the tablet then ?
Also consider that MANY GPS Navigation devices already do it, like the linux based TomTom One.

So... what do you think ?