I've long been looking for a personal holy grail: using Windows Mobile's built-in support for Exchange Active Sync Push to access my information on Google. I had hoped that it would be MailShadowG, but it turns out that service is a desktop-only client that talks only to Exchange. Forwarding gmail to a 3rd party Exchange server is an option, but it's a hassle and doesn't usually provide a very good sync'ed up experience.
Enter NuevaSync [via], a free service that offers an Exchange server that is automatically synced up to Google Calendar and Contacts (Plaxo too, but let's leave Plaxo aside, eh?). They don't have email support yet, but they're working on it and it looks like they're going to do it right -- which is to say they'll be doing it via an IMAP gateway for proper folder sync.
Anyhow, once you've set up your NuevaSync account and connected it up to your Google account, the last step is to set up Exchange on your Windows Mobile phone, you can find those instructions here. Syncing Google's PIM to your device is well and good, but you'll need to also get that info synced from your desktop to Google -- we'll leave that as an exercise to the reader.