If you have a Blackberry phone you have asked this question at least once (maybe thousand times). The BlackBerry phone comes with many fancy add-ons, they have an eye-candy look but there is one problem with them. You have to purchase a data plan for internet access. (As far as GSM services tell) This sounded little weird for me because I could access internet even with my old nokia. The trick is GSM services push you to buy a data plan and BlackBerry also doesn't give information for internet access without data plan, but the phone is capable of accessing internet without a data plan.
I own a BlackBerry Pearl (so the details will be told for Pearl but I guess it applies to most of the models) and I am using internet with my Pearl without paying for data plan. To do this you have to make some settings with your phone. First of all you have to set up your tcp settings. In your BlackBerry menu go to => Options - Advanced Options - TCP and enter your APN information for your GSM Service. You can find TCP APN settings in the list below.
When you finish the settings you need a browser to surf the net. The best one is Opera Mini Browser. You download the Opera Browser to your BlackBerry and in the Opera Browser menu you go through automatic network setup. Once the Opera Browser finds out your settings you are ready to surf the net from you BlackBerry for free. (Excluding standart connection charges from your GSM service provider)