According to Gadgetwise blogger Roy Furchgott, the MobiTV app pre-installed on AT&T and T-Mobile's Samsung Galaxy S lineup would rather have you use 3G network bandwidth to watch videos than streaming over WiFi. This should come as a huge surprise to customers, as most carriers would welcome streaming via WiFi as opposed to using that amount of bandwidth. Considering the possible congestion such an application could cause for those networks, resulting in more dropped calls and slower data streams, one would have to question the motive behind such a move.
This little idiosyncrasy does not seem to be a ploy by AT&T to entice users to upgrade their tiered data service, as T-Mobile still offers an unlimited data plan, but more than likely a quick fix for the developers of the MoviTV application to allow the use of the service over WiFi. Furchgott questioned the developers of MobiTV about the issue, and was told it's all proprietary information between their company, the carriers, and those who own the content. For AT&T customers on the DataPlus plan, YouTube is still available over WiFi.