arnies: Will we have any issues keeping my number if the name on the Slingshot account differs from the Vodafone annount holder?
Will a call to Slingshot beforehand to let them know suffice?
You don't need to talk to Slingshot, just make sure you're not contracted to them else you're responsible for the early termination fee, it should be fine to port your number over as long as you have authority from the account holder to do so.
Edit: Talk to Slingshot after the whole thing is done, and you're all working on Vodafone, only to make sure you've been removed from their billing system, too many customers have been caught out with this.