Universal Locator Code

You're waiting for a shuttle or something like that. But, you have to wait indoors where you can't see it approach. You want a call on your cell telling you to come out - automatically. How? When you've registered at a hotel (say), they give you a code you can use that will be valid during your stay. Then, when you want to be notified, you dial a number on your cellphone and, since the system also knows where the shuttle is, because it's tagged, and it knows where you are - since the cell-company can get your approximate location by triangulation, you can be notified.