Be Excellent To Each Other

I've done some googling, but haven't found any definitive information so I wondered if anyone here knows more.

I'm trying to find out if mobile network operators (Vodafone, Orange, O2 etc.) commonly block TCP/IP ports > 1024, whether the blocking (if it exists) is dependent on type of contract and whether or not MNO's will unblock them (if they are blocked) on request?

For background: I'm involved in the development of a mobile application that will use TCP/IP over GPRS. The idea was mooted that we'd use a high port number and a custom protocol (not my preferred option, I'd much rather shove all the data over HTTP - but there are benefits to the other approach), but before we go along that route I want to be more confident that we're not going to hit a brick wall.

I don't know of any operators that do - and I can't think why they would, either (outside of things like blocking 25). I've never had any issues getting mobile apps to talk directly port->port on O2, certainly - and it's a pretty standard way of doing things.