I'm assuming that this is a just a typo and should be the WRTP54G-AU? i.e. with a P for Phone.
My boss phoned to get some vfx VOIP lines installed using a WRTP54G and was told that this was not a certified device and that he'd have to use Open-VFX. The WRTP54G was one of the first certified devices, I used to use one. Could it be that the WorldXChange staff are checking the website for the certified models and the typo is misleading them?