The E355 is unlocked so free i tested it with the 3 main providers here in NL: KPN, Vodafone and T-Mobile. All work just fine!
I had the best experience after i Placed the KPN SIM; All Settings The E355 needs to connect were automagically added.
If you follow the manual Afterthat You can be online within 5 minutes (incl. Connecting to Wifi, adjusting personal preferences, etc.).
When I start the car, it takes about 45 secs. Hanes E355 to connect to the network, Afterthat every passenger in / near the car has Wifi access to the internet.