Apple released iOS4 this monring. Even though I have less than a week before my iPhone 4 comes in, I decided, what the heck, and updated my iPhone 3G this morning.

My first piece of advice to others who want to do this: don’t expect too much. Two of the most-anticipated features, multitasking and wallpapers, don’t work with the 3G. Among the smaller features, screen rotation lock and bluetooth keyboard syncing won’t work either. This leaves folders and Mail’s consolidated inbox as the top features you’ll enjoy, with a few other small features thrown in that you’ll stumble over in time, like playlist creation in iTunes, or digital zoom for your camera (not worth it).

My second piece of advice: don’t panic. That is, don’t panic when iTunes tells you you have to “restore” the phone; iOS4 on the 3G has to do that–just back up as best you can. And don’t panic when it takes an hour, or more (some people say it took 3 hours)–that’s also normal. Most of all, don’t panic when the 3G seems to freeze or go glacial after your update–it does that, but after a few minutes, it settles down and starts zooming along as quickly as ever.

At least it did with mine. But I had a bit of worry there at first. Right after the restore, the start/unlock screen sat there, frozen, then the phone crashed. Restart: the unlock screen comes up, and the shimmer animation for the unlock slider is maybe 1 frame per 2 seconds, and it doesn’t work. Restart again, and it works, but its incredibly slow–but at least it works, and I can jerkily go from slide to slide. Two minutes later, it has slowly smoothed out and everything works fine. So just give it time.

A warning: after restoring and upgrading to iOS4, before you sync your iPhone for the first time, check the settings–I forgot to do so. All of your music and videos and other stuff are kept through the update and restore, but iTunes then forgets these settings, erasing most of your data upon first sync. It took me an extra hour or so just to put the stuff back on.

I have to say, the folders feature alone is worth it. I hate scrolling across nine screens. I made the first screen mostly my main apps with one folder for important stuff I don’t use every day; all of my games on the second page, the 4 most-played at top and the other more than 30 in categorized folders; the third page with good but not-often-used apps not in folders, and then the fourth page nothing but folders. And then the crap after that. I am finding this makes it a hell of a lot easier to organize things the way you want to, and access a wide variety of apps with ease.

The unified inbox and mail threads seem nice, but I think that’s something I’ll get used to over time. There are other things–the photo app now recognizes faces and places, but I don’t use those usually. When emailing a photo, you get to choose the size now. Stuff like that.

Oh yeah, and it looks like the international store issue is still open–I am able to access the U.S. store from my iPhone just like I am from my iPad, both of which were not possible before May.