The tablet itself will not offer mobile broadband connectivity, relying instead on either a Bluetooth connection to your phone or the built-in Wi-Fi radio. Boy Genius likens the upcoming device to Palm's ill-fated Foleo, which as you may remember was roundly criticized since its announcement and got killed off before it could even make it to market. After all, it offered very limited functionality at a very unattractive price point. Apparently some employees within RIM are well aware of this and have expressed "frustration" that the company would even try such a tablet.
It remains to be seen where all this goes but it would seem that RIM has plenty of work ahead optimizing its operating system and hardware for touch input before trying to market its own tablet. For all the effort the company has put in its SurePress technology, their Storm series isn't particularly known for its prowess in this regard.