The big upgrade to the iPhone that came in June, with the ability to add third-party applications, was huge.
It was also bug-ridden.
Your iPhone 3G likely experienced a lot of dropped calls, short battery life, applications that would crash and suffered performance issues, and a number of other annoying and possibly detrimental problems. Some of those crashes caused data loss, and it wasn't pretty.
Also, the earlier versions of the software claimed more power from the cell towers than they really needed, thus making them available for fewer other users.
The 2.1 software, released last week and broadcast via text message to all iPhone users by AT&T today, addresses many of these issues. In testing, battery life is considerably longer, and many of those performance issues are gone.
For example, selecting "Contacts" from the Phone application or the home screen would take a long time to come up. Searching was sluggish, and using the alphabet along the right side was painfully sluggardly. The new software addressed this.
So, iPhone users, it's time to upgrade, even if you've waited a while.