Same issue for me with Virgin Australia, tried Virgin helpdesk who passed me on to HTC. According to the HTC help desk it is an issue since the recent 4.0.4 update that is as yet unresolved ??? Have tried resets, new APN entry, entering Optus APN data, all to no avail.
The advice I was given, the issue was "escalated" (hate that bull**it word) to a higher level of tech support with no time frame for an answer.