TechCrunch says availability is planned for September and pricing is expected to be in the $350 range. Specs include 1 GB of Flash memory, a 2.5 screen, and 7 hour battery life for talk or web surfing (45 minutes for music). Mylo will be available in black or white.
For a lot of talk- and media-focused users with consistent access to WiFi connections, this device may be a great alternative to more expensive smart phones, UMPCs, palmtop PCs, and yes... even iPods.
Update: techmeme link. Update 2: Added link to the Sony site.