Using Blackberry BIS you can sync your phone email client with any Imap server. I'm using Dovecot running over Arch Linux for my tests.
Everything worked great, but I had one simple problem, none of the emails sent from the blackberry were visible in the sent folder in Thunderbird or the iPhone.
After researching a little, I found that Blackberry expects that a folder named "Sent Items" (without the quotes) exists in the root of your Imap server.
Once I created it (using Thunderbird) all emails sent from the Blackberry started to appear in that folder. Next I configured iPhone and Thunderbird to put sent emails in the same folder and now all my clients are in sync.
It is also good to note that Blackberry does mark as read the emails read in other clients. But the other way it works.
Also the deleted emails in other clients are deleted from the blackberry.