Some providers offer unlimited mobile broadband packages if you sign up for one of the monthly mobile broadband deals that are available. Although these are advertised as unlimited, there is always a cap on any type of package offered. The only difference is the cap for the unlimited package may be an unusually high figure. However, this package is for serious users of mobile broadband.
Business users are also offered various types of business mobile broadband packages again based on the usage pattern and download limits. However, if you are going abroad on business trips, clarify the rates you will have to pay overseas, as there could be a massive difference in tariffs.
Speed of a mobile broadband service is another factor to be looked at before settling for a service provider. In the UK we can expect the mobile broadband speeds we enjoy to steadily increase. When 4G is introduced we can really expect it to soar. The government department in charge of broadband is the Department For Culture and Media and you can visit their broadband regulatory site here. Since the service is wireless, there could be issues like buildings and trees acting as signal blockers. There is also a possibility that the Mi-Fi signals lose their strength as they enter your building, and you may not receive an adequately strong signal. It is best to make a trial of which provider has the best signal in your area.