I have already talked about my G1 phone. This phone uses gmail by default.
I configured my gmail account to get the email from my critical accounts, the I would see the mail on my desktop using Thunderbird, I could also read the mail from my g1 and on the web using gmail. I was already using my gmail calendar on my phone and Thunderbird.
One thing that was not working real well was the indication of messages being read on my phone. When I would look at the messages I may have a hundred that I alread have read and processed on my desktop. I would use gmail on the web to mark the messages as read to try to manage the situation. Then it hit me I should access gmail from Thunderbird using the IMAP protocol. With IMAP the messages stay on the server, you see the messages and folders on the server through your email client. This works quite well, as I read the messages they get marked as read. One extra advantage I did not think through is that my deleted items, and sent items are on the server so I have access on the web or on my phone. About the only drawback is that the messages are on the server rather than downloaded to your machine. This means that as you click on the message it downloads from the server, so there is a lag for large messages, if you use pop3 this takes place when you do a send and receive so the messages pop up.
I found another plugin for Thunderbird, Zindus. This plugin synchronizes your contact list between Thunderbird and Gmail. Now I have the same address book on my phone, gmail and Thunderbird. This is what I have been searching for, an address book that works on the desktop, web and my phone, I no longer have to try to update three different address lists.
Overall I like the process. I get notified of new email messages, I can read them on the phone and reply, and I have all this on my desktop when I get there. If I can not get to my computer I can also use any web connection to the Internet.