I've never done mobile dev. I get the problem, but what's the preferred alternative? For, say, email, sports scores, VOIP messages, stats dashboards, etc?
Apple provides push notifications, which work similar to SMS messages, in that your server can push data to the device without needing the device to poll, due to deep integration with the lower level cellular whatsis. I think Android has something similar as well, but I'm not completely familiar with it.
Basically, IP over 3G works pretty well overall but can be a real battery hog, and dropping down to something more native can be a big win. Cellular radios are built to use very little electricity while monitoring for a wakeup call from the tower they're connected to, so if you can take advantage of that like push notifications let you do, then you'll do a lot better.
A somewhat less wonderful alternative is to keep a persistent TCP connection open with a very long timeout, with the remote end sending a notification to wake up the phone when needed. You'll have no traffic most of the time, and the wakeup being initiated from the remote end removes the need to poll. I believe this is how Skype (and other VoIP apps that allow incoming calls in the background) works on iOS.
Edit: I forgot another technique that some iOS developers have used: register with the "significant location change" API, which can be used to wake up your app when the cell radio switches towers, and then check for new data then. This is technically an abuse of the API (which is intended for when you actually need to know about location changes) but works well enough. It can help to e.g. ensure your stuff is recently synced before the user goes into the subway and beyond data coverage. Once again, this is using low-level cell radio stuff to avoid overtaxing things.
