Unlike the DNS and the DNS hierarchy, we do not have a HLR hierarchy. By the way just for record , all the updating of those register, databases or whatever you want to call them is done via connectionless transaction protocols. The thing that differs is that in mobile IP the traffic goes always through the home net , when he is away. In contrary with mobile phones, the traffic goes directly to the foreign net without passing through the home net. This indicates that a relation of names to numbers is sometimes hard to make.
Computers are better at playing with numbers than with names, especially if speed is of the essence.
As interworking between a telephone net and the internet is more and more becoming a issue, so a DNS lookup or related database query may be in the cards.