It is anyway time to upgrade to an iPhone 5.
I still roll with an iPhone 3GS as I have a 2-yr contract I did not upgrade to an iPhone 4 when it came out. Now I do not want the iPhone 4 anymore and wait out until the iPhone 4S aka iPhone 5 comes out in September.
Apple already left behind the iPhone 3G. The iPhone 3GS is though still on sale and is the "bargain'' iPhone in the United States for $49 (w/ contract).
How To: Buy a Pokemon Go Plus
I honestly do not care as with the iOS 5 release comes a new iPhone. Those who jump on the $49 iPhone 3GS deal now should think twice about it though, unless they are fine with the current features.