So, reluctantly I started looking for ways to get back to tethering with Telecom and was lucky enough to find this site and its instructions for how to do this.
Unfortunately I believe this has involved 'jailbreaking' my phone using the blackra1n software but desperate times mean desperate measures! I have now got tethering back and posted this message via my iPhone. The process was incredibly painless in that I simply installed blackra1n, installed the
sn0w application on my phone and it reset and voila! It may have been that because I had already installed the IPCC file that was posted on Geekzone that I didn't have to change any other settings as that is all I have done. I will post an update after a few days if I have any further problems but am really pleased to be back in the world of mobile broadband via XT as the Vodafone's mobile broadband is sooooo sloooow!