If you just switched to T-Mobile, it can take a bit for the data to activate.

Just to make sure, your apn is set to epc.tmobile.com with no username or password, correct?

Also, are these gamesaves being viewed as read-only by the PS3, N900, Windows PC, Mac, Linux, etc?

I don't know why your pictures wouldn't save unless the PS3 tried to format the memory for itself and now the N900 doesn't have write permission.