I still use my Sprint HTC Hero as an Wi-Fi enabled Internet device. Everything I could do before I switched the cellular service to my Sprint HTC EVO 3D still works, except the whole making telephone calls and text messaging thing.
In fact, if you root and flash an Android 2.3 ROM to your old handset, you could use SIP calling. That, coupled with Google Voice for text messaging, would make it a great home telephone.
