I just bought my first iPhone, a 32 GB iPhone 3G S, and found that that there is an abundance of information out there covering just about every aspect of its use. As an iPhone virgin, most of this is new to me, but I'm sure it's old hat to most.
Apple, however, is set to sell over
I tried making a ringtone from iTunes, but when right-clicking on a song and choosing 'create ringtone' I found that only songs purchased from the iTunes store could be used, at least in iTunes 8.2. In reality you can make a ringtone from any MP3. You can find the easy steps here.
Double Contacts and Calendar Entries
After setting up MobileMe and syncing my phone the first time, I found that all my contacts and calendar entries had been duplicated so that there were two identical entries of everything. Our own Chris Rawson set me straight on fixing this. If you disable calendar and contact syncing from the iPhone, all the information brought in from MobileMe will vanish. Next, re-enable them and you will be asked if you want to merge the contact and calendar information with what's on the iPhone (which was brought in by iTunes). You do. And in doing so, the problem will vanish. This tip is not just for iPhone 3G S owners, it's also happened to previous iPhone users who updated to system 3.0.
Period Space Bar Trick
When writing an email, typing the period key on my iPhone 3G S often does weird things like jumping down a line or two, slowing me down to a crawl. Chris Rawson also came to my aid by telling me that when you reach the end of a sentence, double tapping the space bar displays a period. This is much quicker for me, and my typing is cleaner. I'm not sure about earlier iPhones but for the iPhone 3G S, this must be set up manually. Go to settings-> general->keyboard and turn on the "." shortcut.
There is no need to pay Apple $69 for AppleCare. I've been buying AppleCare from eBay at a decent savings for years. Often you don't get a full box, just a paper with the registration code, but I've never had a problem. Right now you can get AppleCare for $42 including shipping.
What have you found? If you have a problem or question and are too bashful to ask: ask here and we'll put our hive-mind right on it.