A couple of points:
- the 6000 release in Europe has been confirmed to be using the 2002-era GPRS technology. Tomtom has used GPRS on all their LIVE products, and this is unfortunately continuing. GPRS is horribly inefficient with data spectrum (think 9600-baud dial-up modem vs DSL on the same phone line). So at the slightest amount of congestion, carriers shut GPRS down, as one disabled GPRS customer frees up space for tons of 4G customers. So GPRS tends to fail during congestion (eg: large traffic jam) just when customers need it most.
- AT&T has committed to Tomtom that they will not do this congestion-based shutdown on existing GPRS towers in the USA, however, they have not built new GPRS towers for the past couple years and will never build another one. So when the old GPRS tower in a neighborhood is full, a Tomtom can't use the 3 shiny new 4G towers right next to it. Furthermore, AT&T has announced a full GPRS shutdown in 2017.
- Tomtom and AT&T have been doing substantial drive testing diagnosing all of the 2011/2012 outages. It turns out that much of it was due to bad software/tuning on Tomtom's PNDs and servers. Tomtom corrected this in late 2012, and their connected devices in the USA have been much more reliable since.
- Regarding bluetooth data, my understanding is that many of the car radios use custom apps on the smartphone that use bluetooth to relay signals to radio software. This is the same tactic employed by Garmin on their latest round of connected devices. Often, this approach prevents the carriers from requiring hotspot-addons to a customer's account in the USA. On the other hand, Tomtom uses a standard-but-rarely-used Bluetooth PAN protocol. This protocol requires no phone app to be installed, but often requires the purchase of a hotspot-addon plan for a phone carrier to permit its use.