Anything interesting you can do with an iphone?
Here’s one I learned from a coworker: if you double click the home button, you access a type of “task manager” that shows you all active programs. If you hold down one of the icons, they wiggle and then you can close them, saving memory and battery power.
What’s yours?
You have a 3GS, right? Have you tried the voice control function? You can command your phone to dial any number in your contact list. You can also control the iPod with yur voice. You can command it to start and stop playing music. You can specify a particular artist, album, or playlist to be played by just speaking into the phone. Very good for use while in the car, so you don’t have to look away from the road. Almost like the SYNC in some models of Ford cars.
I have almost never gotten the voice control to actually play what I want. Haven’t really tried it for dialing though.
The task manager is good for misbehaving apps. Sometimes when one isn’t working right, you can fix it by killing it in the task manager so it is forced to restart.
When shooting video with the iPhone 4, you don’t get a wide angle because it gets 720p by cropping the 5 megapixel image, and using the center of the image for video. It tends to look even more zoomed in because it defaults to showing you 4x3 even though you are shooting 16x9. You are actually recording more at the edges of the frame than you can see. If you double tap the image while in video mode, it will switch to letterbox so you can see the whole 16x9 image you are recording.
Settings -> Mail, Contacts, Calendars -> Fetch New Data -> Push -> “Manually”
I just saved you 2 hours of battery power a day.
I don’t know about closing apps to save battery - generally, “sleeping” apps aren’t running at all, unlike earlier “multitasking” apps.
Press the home button and the sleep button to take a screenshot! Just press and release, don’t hold (or you’ll activate the manual power-off).
You can add an extra field to any contact in your contact list- “phonetic name”. Basically, it allows you to tell the iPhone how to pronounce- and understand- that name. My friend’s name is non-standard, so the phone could never understand me when I told it to call him. I put in a phonetic pronunciation of his name, and now the Voice Command understands me perfectly when I tell it to call him. I just wish I could do the same with my music.
Also in Contacts, you can “link” contacts together (it’s down at the bottom). It allows you to make a “Family” contact card which kind of contains all of the members of that family. My sister and her husband share one family card now, and it automatically took the information they have in common (address, home phone) and put that on the their family card. They each have links in that card, though, so if I want to call my sister, I can just select her link.
Google Voice and Talkatone Apps give you free texting and voice calls over WiFi.
After your contract is up, if you want to give up 3G data (and use only WiFi) but still make calls on a pre-paid plan, you can buy a GoPhone SIM at any ATT store and use it in your iPhone
A question. I have an iPhone 4, running version 4.2.1. Is an untethered jailbreak available? I’ve used Redmondpie.com before, but it’s not clear if it’s untethered.
Have any of you jailbroken your 4? I don’t really want to google and use “Joe’s House of Jailbreak-orama”, but use a technique/website one of you have tried and worked.
greenpo1son hacked it.
YMMV, of course, but I have no trouble commanding the iPod with the voice control. I just now randomly commanded it to play a Paul Simon playlist, the album “The Lonesome Jubilee,” and artist Bachman-Turner Overdrive, and it understood me perfectly, although it repeated BTO back to me as “Batchman-Turner Overdrive”. 
I have enough confidence in it to use it while playing music through my car stereo (although I limit myself to using it while I am stopped at a red light or otherwise while the car isn’t in motion).
I like the jailbreakmatrix.
You can hold the home button and press the sleep button (in other words you don’t have to time your press of both)
I was quite pleased when I found out how to take screenshots 
Enable the setting to do this, then you can double tap the on-screen keyboard space bar for a full stop (period), space and capitalised start to the next sentence.
Hold down on-screen keyboard keys for alternates. For example, holding down letters gives you their accented versions; holding down the default currency symbol gives common alternatives; and where you have an email address field, holding down ‘.’ allows you to select from default suffixes (.com, .co.uk, .net, .org and so on).