I've used ABF UPack for two cross country moves and have been very satisfied with their service. In fact, I recommend them to everyone I know who is contemplating a long-distance move.
The first time I used UPack they dropped off a trailer, which we packed ourselves and then put up a bulkhead barrier. They leave the trailer with you for 3 days to load it and then 3 days on the other end to unload it.
For our recent move we got one of their ReloCubes - which works basically the same way except that all the space is yours and you lock it with your own lock.
The staff at the Phoenix location are very professional and helpful. The driver that dropped off the ReloCube after we arrived was very friendly and even gave me some tips on local places to check out since I was new to town!
It is a great way to move long distance with out have to worry about driving a big truck or towing a trailer. And its very affordable in comparison to full-service moving companies.