I have an N1 from vodaphone and it wasn't locked, it is a common misconception. I put a T-Mo sim in and it worked straight off. However the rom that is in these is not a standard rom and if you want it to accept the OTA updates from Google you need to flash a standard rom 1st.
Taken fron XDA Nexus One Wiki, FAQ
- Q13: Is Nexus One carrier-locked? Will it work with my carrier / network?
A: There is no such thing as carrier-locked N1. All the rumors of carrier-locked N1s, including bits of misinformation from SFR/Vodafone, are untrue. Unlocking the N1 refers only to bootloader, allowing to flash custom ROMs freely, and doesn't concern non-existent carrier lock. There are 2 types of N1: 1) T-Mobile version, the standard one - works with 900/1700(AWS)/2100 MHz bands, 2) AT&T version, works with 850/1900/2100 MHz bands. To know if N1 will get 3G reception with your carrier, check the model you're getting and List of UMTS networks, and see if they share the same frequency/ies.
Edited by 900i, 30 April 2011 - 01:51 PM.