Update: According to a Sega Sales Representative, Phantasy Star Online will definitely not be compatible with Sega's broadband adapter. However, Sega Representatives have been giving conflicting reports to various websites all day. RPGamer will bring you Sega's official word as soon as it is delivered.
After some initial fears that the upcoming online RPG for the Dreamcast, Phantasy Star Online, would not allow play with Sega's broadband adapter due to mixed messages on the subject from Sega, IGN Dreamcast's Brandon Justice had the chance to talk with a Sega employee with close ties to development. It was thus revealed that Phantasy Star Online will allow gameplay with the broadband adapter, but Sega will not be able to offer any support for it. Additionally, Sega will not guarantee that playing with the broadband adapter will be a bug-free experience.
Though this may be disappointing news to those looking forward to a bug-free broadband experience, keep in mind that this news implies that Sega simply did not have enough time to thoroughly test the two products with each other and that any problems experienced will probably just be minor bugs. Sega is expected to make an official announcement about the situation soon. RPGamer will keep you informed as the situation becomes clearer.