I'm playing with a new app on my phone right now--
Soda-Pop Mail. It's a BREW mail network that allows you to check your mail from almost any POP3 network (including Hotmail and Yahoo!). I only downloaded the demo, which is good for 2 days...surprisingly, it only cost $3 for unlimited use, but uses airtime. I can't justify getting it on a permanent basis yet. But it's a pretty cool little app.