Slingplayer on 3 network

[Guest coercri]

I've been testing the 3 network with a pay as you go SIM to see if it gives a better signal for my Desire, but I cannot connect to my Slingbox. If I pop back in the T-mobile SIM all is good, so the config is ok, it is just 3 blocking it.

Is this a known problem on 3; do they block this port? Is there a work around for it? Would it be ok if I got a contract SIM from 3?

Thanks in advance.

Ps. It's a WAY better signal than T-Mobile - in Shropshire anyway!