We wouldn’t be surprised if the next rumor to spread about the Nexus One is that it will be initially in beta, like all of Google’s products.

But for now, Engadget reports that the phone will be available only by “invitation,” just like how Google (NSDQ: GOOG) slowly provides access to other services, like Google Voice and Google Wave. Details on how the invites will be passed out are not clear, but potentially, developers may get priority. After the invitation period expires, T-Mobile will apparently sell the phone, which once again sounds like a fairly traditional mobile-industry relationship. It’s still really unclear whether the Nexus One is the “Google Phone,” or just another phone running the Android operating system.