Virgin Media are in the process of changing over to what they term 21CV, which uses your broadband connection for the phone - it's very similar to VOIP, but the technical details are a little different, but not in any way that matters to you or me.
Do you still need a landline? You say you've got a mobile, if you use a phone & provider that offer wifi calling, then you could use that, choosing a package that gives you unlimited calls (eg if you use little or no data, then an iD Mobile sim for six quid a month fits the bill).
If you do want a VOIP line, then consider Vonage if you want bundled calls. If you just want a cheap as chips VOIP line then Andrews & Arnold will offer you a VOIP connection for peanuts (£1.20 a month). Outgoing calls are charged, but at decent prices, the main downside is that you'll need to have a chat with them about getting things setup, and possibly configuring the Analogue Telephone Adaptor that's needed to sit between your hub and your landline handset.
And if you're unimpressed with VM's attitude and service, why not look for a new deal with somebody else that includes the things you want, but not the things you don't? What about Zen Internet? They're a good balance between price, ease of dealing with them and service. If changing provider, don't cancel VM until the new service is connected and working - better to pay for an overlap of service, than be without service if the new connection gets delayed, eg by strikes.
