Linuxluver:

nefnee: if that is true, then why does telecom say that it is possible to bring vodafone phones over to the xt network?

If you have a Vodafone phone that supports 3G (WCDMA/UMTS), then it may be possible to use it on the Telecom XT network, but on the WCDMA 2100 frequency ONLY.  Telecom XT supports WCDMA 850 and 2100. They do not have GSM at all. So the quad-band GSM (850/900/1800/1900) is absolutely no use with Telecom XT.  

The lack of GSM on XT is what limits any Vodafone phone to just two frequencies (noted above - WCDMA 900/2100)....and Telecom do not use WCDMA 900. They use 850. Trying to exist on 2100 alone is a real challenge as coverage is very patchy. I have Telecom XT coverage on WCDMA 2100 at home and at work, but it drops out frequently in between. It's just not reliable as the sole frequency for a Vodafone phone to be used on. 

But the iPhone DOES support WCDMA 850 and 2100, so in many ways it is better (for 3G) with Telecom XT than Vodafone......but Telecom lack GSM, which the iPhone also supports...so your access will be more fragile as there isn't the layer of older, reliable GSM tech underpinning the WCDMA.  

Hopefully I;ve repeated the same points over often enough from different angle to get you to the point where you understand that:

1. GSM is 2G and is on 850/900/1800/1900.....and ONLY works with Vodafone and 2Degrees. 
2. WCDMA (3G) is on 850/2100 for Telecom XT and 900/2100 for Vodafone and 2100 only for 2Degrees (when they get around to launching it - which they haven't yet). 

You might think; "Yay! They all do WCDMA 2100!"...and they do....but for 3G, the largest areas for Teleom XT and Vodafone are covered by the 850 and 900.....and the 2100 is used as in-fill mainly urban areas. So if your phone can't do WCDMA 850, then even if it can do WCDMA 2100 it will be a poor choice as a Telecom XT phone as coverage will be very patchy in cities and almost non-existent on the highways between them and in smaller towns.

Telecom XT not having a nationwide GSM network is the final straw that makes GSM-only phone completely un-usuable on Telecom XT.