Does the Tomtom Go 720 tether via Bluetooth DUN or PAN? Either one should work, but not out of the box. Depending upon which profile the Go 720 supports, you'll need to at least edit one system configuration file, and you may also need to create and run a small script. Please see "Fremantle Unsupported Bluetooth profiles".

From what I've seen, thus far, tethering to the N900 hasn't been widely tested with a wide range of devices, so there may be other, yet unknown little gotchas requiring work arounds. If you attempt to tether your Go 720 and run into trouble, please post a request for help.