(Although personally I could swear I've had a gmail account at a custom domain since even earlier than 2006. Originally via some kind of partnership with... Dreamhost? Something like that? Anyway).
http://googlepress.blogspot.com/2006/08/google-launches-host...
> Google will provide organizations with two choices of service.
> A standard edition of Google Apps for Your Domain is available today as a beta product without cost to domain administrators or end users. Key features include 2 gigabytes of email storage for each user, easy to use customization tools, and help for administrators via email or an online help center. Furthermore, organizations that sign up during the beta period will not ever have to pay for users accepted during that period (provided Google continues to offer the service).
> A premium version of the product is being developed for organizations with more advanced needs. More information, including details on pricing, will be available soon.