June 6, according to Sprint's announcment today (May 19). The phone will retail for US$199.99 (after a US$100.00 mail-in rebate), and will be available in Best Buy, Radio Shack, and select Wal-Mart stores, as well as Sprint brick-and-mortar outlets and Sprint.com.
You'll be expected to spring for the traditional two-year contract and either the Everything Data plan or Business Essentials with Messaging and Data plan (both US$70.00/month and up). Still, Sprint argues these plans will save Pre early adaptors up to $1,430 over two years vs. comparable AT&T and Verizon plans for smartphones and PDAs.
Interestingly, the release date is both a Saturday (attention, shoppers!), but also two days before Apple's WWDC, at which announcements regarding the next-gen iPhone are strongly rumored.