It all depends which area of consulting you want to move into, level and the type of role you want to do. I'm currently doing an Executive MBA at Lancaster, with a BSC Comp sci background.
Here's some advice from someone working in IT consultancy:
PhD: A threat to most managers around you: Being percieved as smarter than others around you, especially those that you report into- can work against you. Its great if you intend to work in a research consultancy / firm eg. Gartner
MBA: The MBA allows you prove simply that you can think outside the box. Some percieve it as a ticket to upper management. Its generally more respected in banking sectors. However, strategy consultants often have MBA's. The MBA combines research with industry analysis, which makes it more useful.
Hope that helps.
Oais Ahsan UK