I had an open-ended Tripple XL discount (or something like that), as long as I did not downgrade my package. I'd had it for almost 3 years, I think, until last December when I did change my package to a V+ box and 50 MB broadband. I get the same level of discount but now it's called a loyalty discount (or something like that). This discount should also be open-ended - guess I will find out soon if it is. It does get eroded by price increases though, as the discount itself does not change.
iTekweni, I was offered the Tripple XL discount but when I had called up about upgrading I stressed that I would only upgrade if I could keep the discount and VM were very obliging. I do not know what package you have but if you wanted to upgrade you could always say that you are looking at Sky's package. I had got a new HD TV but only had the old TV box so I'd said I was looking for HD content and was comparing the two. I did not have to haggle, they just offered me the discount and I thought it was fair so I accepted. It's only a phone call so you have nothing to lose.