I just change the APN to 3internet from three.co.uk which gets rid of the censoring. Settings / Wireless and networks More / Mobile networks / Access point names on my Nexus S.
So far (nearly two years) no ill effects with billing, I'm on the one plan which allows tethering YMMV.
The only gotcha I'm aware of is that bits of three infrastructure such as the MMS server and I think the "mythree" stuff don't recognise the phone anymore but thats no big deal for me. So the couple of times I've received an MMS I've changed the APN back.
So far (nearly two years) no ill effects with billing, I'm on the one plan which allows tethering YMMV.
The only gotcha I'm aware of is that bits of three infrastructure such as the MMS server and I think the "mythree" stuff don't recognise the phone anymore but thats no big deal for me. So the couple of times I've received an MMS I've changed the APN back.