Chatter Beta (Treo 300 and 180/270) will begin on or before March 17th. Anyone interested should go to the Chatter Forum (URL below) and fill out the questionaire and review the license agreement.

In the meantime, I recommend that anyone interested in using Chatter with IMAP eMail and who doesn't currently have an IMAP account, check out Basic accounts are free; if you want to use SMTP through them for outgoing mail, you can upgrade for (I believe) $15/year. I've been very pleased with their service for the past five months.