i bought an ls model a couple of months ago also and the salesman pushed the onstar button and we set it up right there at the dealership(unexpectedly i might add kind of put me on the spot , my car asking me to set up passwords an user names and such)
any way my data just expired and ive been having a heck of a time trying to purchase more, website says its having problems and you may need to call.
your ls should have it though,guess you will have to call or go to the dealer.