I have to say that the only thing that has ever really bugged me about VM is their standard call charges.
Last year I upgraded to the XL Phone pack as part of a good service upgrade deal, but I still have had to route some called, mostly 0870/0845 and mobiles, through a 3rd-part provider -
www.18185.co.uk - in order to save some money.
As you can see from the attached graphic*, which doesn't include calls to mobiles, VM's call charges remain substantially higher than BTs.
I realise that calls is there 'cash cow', which is why they discount so heavily when you take their phone-line, but I really think it's time they did something to address the problem.
I did try to move onto their Talk200 pack but it meant losing too much discount to make the move financially viable.
* Based on slightly old figures now, I know!