Obtaining an Alien registration number?

[edugdale]

I am an alien resident in the US on an H-1B visa and applying for a green card through a family-based application (my wife of 18 months is an American citizen). The USCIS website that these applications don't need to wait for an Alien Registration number to become available and says that I can send in on all the forms at the same time (I-485, I-130, I-864). But all of these forms ask for the Alien registration number. Am I supposed to get a number BEFORE I submit my proposal and, if so, how do I do this?

Many thanks for your help!