Hi,
Yes, the X800 can be used as a modem with a laptop.
Please check with your Network what tariff restrictions are in place, as many basic data-plans activated on phones are for phone browsing only and do not cover use as a modem with a laptop.
There have been a couple of horror stories recently in the press of people downloading vast bittorrent traffic and the like and running up enormous bills.
Also, VoIP use is not supported by many data plans officially, so be careful.
Regards
Ivan