The event will take place in California at 10am tomorrow (6pm UK time) for US journalists, with nothing so far planned for UK press.
Google has kept the phone a closely guarded secret, but unconfirmed reports about its specifications and how it will be sold have cropped up on technology blogs such as Gizmodo and TechCrunch.
According to , which is carrying screen shots of what it believes are landing pages for the phone, Google will sell the Nexus One direct and unlocked to any network. It will cost $530 (£327) from Google but can also be bought from T-Mobile on a two-year contract for $180.
In addition, an , which Google handed out to employees before Christmas, was posted on December 30 on Daily Motion.
The phone is manufactured by Taiwanese company HTC and carries Google's Android mobile software.
Alongside work on the new phone, Google, in November, acquired mobile display advertising firm AdMob for $750m, subject to regulatory approval.
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