I too spoke to HTC this morning on behalf of my girlfriend (problem as above). Couldn't have been less helpful and the guy I spoke to "hadn't come across this as a problem"! I mentioned both this and another forum where the problem had been highlighted, but that cut no ice.
His suggestion (for a phone that has only been owned for a week) was to try a different SIM card (even though the SIM was working perfectly well in the Sony Ericsson it was transferred from), speak to Vodafone or return it to HTC for a repair. I mentioned the software update issue but this was ignored.
Phoned Vodafone, who were slightly more helpful, but they said that the best thing was to take the phone into a Vodafone shop and have them check it over and, if necessary, replace the phone or the SIM card. We'll do this and see what happens.
Not happy with HTC at all.