I have a UT Starcom PPC-6700 SmartPhone, through Alltel, that I use essentially for running my small business.  Alltel's data service add-on (~$40/month) gives me unlimited Internet access with the device, so I can Google search, watch the weather radar from the boat, check email, and get notifications of messages left on the company voice mail system. 

On the email side of things, I have the device synchronized with an Exchange server running in my office.  I can 'force' the device to sync with the server whenever I feel like reading email, just by clicking send/receive in the phone.  With Exchange Server 2003, I can also enable Microsoft's 'Direct Push', which keeps the phone synchronized with Exchange in real-time.  There are plenty of articles out there on how Direct Push works, so I won't regurgitate that here, but essentially as messages come in, they're 'pushed' directly to the phone, so I always have the most recent message list in my hand. 

One significant problem I've noticed is that with Direct Push enabled, the battery life on the PPC-6700 is slashed severely.  I can expect that if I take the phone off charger at 7am, it will be dead (powered off dead) before 5pm.  By contrast, with Direct Push turned off and me synchronizing manually 3 or 4 times during the day, the battery will last 3 days pretty easily. 

It's weird, because Direct Push is touted as a technology that should save battery life.  Instead of the device connecting on a schedule – say, every half hour – and downloading '0' messages while wasting battery juice, it's supposed to be 'smarter' and only connect when there are messages to download. 

I can't find the article now, but one writer suggested that if you don't want your device connecting a hundred times a day and downloading messages, don't receive so many emails!  I would agree, but I think the problem is bigger than that.  I think the problem is with spam, and here's why:

Most of the time, when I 'force' a download with the phone, it will say something like “Email: 0/8” in the phone's Messaging status bar.  When it completes the download, though, I might actually only see 1 or 2 of those messages in my inbox.  I'm left to assume that the other 6 or 7 were spam...and that the Exchange spam filtering rules don't get applied until the download is requested.   

If that's true, then something similar is probably happening with Direct Push enabled.  The difference, though, is that Direct Push is causing as many as 8 connections to (downloads from) Exchange to accomplish the same thing.  Essentially, it's connecting 8 times, and each time it's just running the rules and putting messages in the spam folder...it's a wasted connection. 

[EDIT 2007-05-23]

I almost forgot.  One other problem with enabling Direct Push is that people who call me often get sent directly to voice mail.  The phone never even rings, because the line is tied up with the data connection.  Since the phone spends so much of it's day connected to Exchange, this becomes a problem - think 'teenager tying up the phone all day'.