Why use one now? Because these models are still useful phones. I use mine as a backup phone, for use when friends or family damage or lose their primary phone.
Both models are GSM-centric and have 3G radio chipsets, so they're still great for phone calls. They have GPS, so they're useful for mapping and navigation. And you can use them for texting, of course.
They're also inexpensive. For under $50 you can find a great one that you don't have to worry about losing. You can keep one as a backup phone, or as a loaner.
Of course, you'll want an unlocked one, so that you can use it with any GSM provider.
The Reasons for owning an iPhone 3G or 3GS:
- Super-inexpensive, perhaps $50 for a fine 3GS.
- A great backup phone if your primary phone is lost or damaged.
- A great phone for international travel - as all iPhone 3G/3GS models are GSM.
- A great "first phone" for a kid, so you don't have to worry about them carrying, breaking, or losing a much more expensive device.
- They're stuck at an older iOS level, so they can't run apps that require a more modern iOS.
- Neither model has a front-facing camera, so video chat is not a possibility.
- The iPhone 3G does not support iMessage. However, the iPhone 3GS does.
- Significantly slower than a modern phone for the web.