While you can buy it unlocked for $530, you will be unable to run it on AT&T’s or Sprint’s 3G network. The Nexus one currently supports the 3G radio frequency of T-Mobile in the United States.
Google recently filed an FCC for a version of the Nexus One with WCDMA Bands I, II and V, which are the bands of AT&T. If you tried to use the Nexus One on AT&T, you will be on Edge, or even 2.5G. BAD!
What about Sprint? A user sent an e-mail to Customer Solutions, and got the following answer:
Thank you for contacting Sprint regarding the nexus one.
Unfortunately, this handset model is not on offer as of now.
Once it is launched, you will see promotional campaigns related to the
launch date, cost and the features of the handset on our Web site and
other promotional media.
Thank you for showing interest in our products & services. Please let us
know if you would like us to assist you with anything else.
The response includes that it isn’t available for the time being, but will launch soon.
I personally think it’s a great idea to release the Nexus One with different carriers, and different frequencies, so people aren’t forced to buy the T-Mobile 3G version. And a great source of revenue for Google, I guess?