There needs to be testing on specific devices because application porting does make a difference depending on the handset; also you have inconsistencies with how devices map or handle data, you have 2G and 3G devices as well as the network playing a roll. Certificates are important and how they're dealt with on devices, trusted and preferred.
We've found that applications which are ported to at&t devices which were tested on other networks or other devices do not always function as expected.
