I have the same issue.
After TomTom establishes a DUN connection, I cannot use my phone for any data service until I either reset the phone, or turn flight mode on, wait a few seconds, then turn the 'phone' back on. This ends the DUN call.
There doesn't seem to be a timeout period that I can determine for a DUN call. So, when one is established, it never seems to hang up.
Aside from that, I'm still happy to have the functionality restored. My TomTom is happy, even though my phone can't update its email...
