They use a local GSM network. The sales price includes one year of 30hrs/month of network use, but as the device does not have any significant offline applications and capabilities, that is pretty much synonymous with use in general.

With their German service, you have to pay 45 EUR for each additional year, and 10 EUR per month for time-unlimited use - but as they restrict you to their data-compressing proxies and their specs mention "average use", you should expect bandwidth limits if you are a power user.