The different phone companies have certain restrictions on how their phones are used. This is because they make more money off the restrictions. Like to text and exchange pics uses data. They want an extra fee for that use. The communication programs circumvent their 'pay' programs for use.
Certain games use so much data that they limit the amount of data that can be used (either per hour, day, month)
People have found out how to actually enter the phones programming code and alter the lines of code which remove these 'blocks' which are on the phones.
Remember that at some carriers (att and Tmobile) they don't have these restrictions on use. You either have full data or you have none with them, Other carriers have MB usage limits per month. Jail breaking a phone 'hides' these limits.
Now for the down side. If you re program your phone wrong it is useless, and they won't honor the guarantee. it's at your risk.