Speaking as an end user, I see both sides here. If I call IT it's because I am at a standstill and unable to get my work done. I'm in no mood to go search through a self-help portal, and if IT asks me to, I'm probably going to react poorly! That said, if I already have experience with the system and it's very well organized, I can see using it for less-urgent matters. However, at the same time, I'd be leery that success of a portal will result in fewer IT people there to help in those emergencies.
And, shouldn't routine items like moves, adds and changes already be automated?