Many mobile phone tarrifs, not just Virgin Media's do not include non geographic 08xx type numbers within their "inclusive" or "free" calls. Thus you can end up with a charge and in some cases this can be higher than a standard rate call might have been. It is a bugbear of mine that companies that conveniently use 08xx numbers don't advertise a geographic number too. Maybe because some of the 0845 (supposedly local) and even national numbers can actually allow a payback to the call receiver

for say no to 0800