One of the main reasons people are reluctant to use mobile internet on a regular basis is said to be the cost of data over CSD,GPRS,EDGE, UMTS etc. Not necessarily because data traffic is expensive, but rather because people are not sure of the cost due to the carriers complex price models. The European Union has, by the EU Roaming Regulation , made an effort to reduce roaming charges. However, this regulation does not include roaming charges on data traffic. This means that it is up to the mobile operators to charge as they like for data traffic. In some counties the data traffic can be as high as 12 Euro pr megabyte. [edit: just found an article from Times Online] Fortunately some carriers have seen this problem as well.
So, the least we can do as developers is to keep the data traffic to a minimum.Here are some basic tips.