There's a lot of uncertainty about how the merger will play out for Virgin Media Mobile customers. From a commercial perspective, the existing VM Mobile business will have to be folded into the much bigger O2 business. Whether that happens within a new two year contract nobody can say. Likewise the Vodafone service provision - lots of ways that can be addressed, and eventually all VM Mobile customers will be on the O2 network but nothing firm that anybody is going to commit to over the next couple of years.
There are a few incentives for existing VM cable customers who take VM Mobile, but if you're looking for any material discounts then (whilst they might exist) they'll be few and far between. In the ISP market, VM have a differential they can use to push higher prices (speed). In mobile, the market is cut-throat, and margins are thin. The nearest to any differential is if one operator by chance has better coverage for an individual customer's home or workplace. All of which means it is very difficult to offer a discount without losing money.
And see page 6 of this. With the job losses and restructuring from the merger VM Mobile service is probably going to get worse not better. That doesn't mean you'll have any problems with VM Mobile, but it's worth considering that like for like, five times as many VM Mobile customers felt the need to complain to Ofcom as did Sky Mobile customers. Looking at Which? data, the top mobile providers were Giffgaff, Tesco, Smarty and Sky, and VM Mobile came second from bottom with Asda. O2 were the best rated "own network" provider by Which?
Usually makes most sense to buy your own handset, and then have a rolling one month SIM only deal. That way you're not tied to an operator if things do go wrong. I'm with ID Mobile (sim only) and you'll see in that link that they have the worst complaints performance of all companies covered according to Ofcom, though Which? rated them as middling. I've had no problems at all with ID Mobile, and they offer the best online account management I've come across for mobile phones, although I've not tried Giffgaff or Smarty, but if the worst comes to the worst I can bail out in less than a month, and without the need to speak to customer service agents.
Choose wisely!
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click Mark as Helpful Answer or use Kudos to say thanks