You ask,
Is there a 640x480 PDA with WIFI, GPS, GSM/GPRS?
If you don't need the phone, or are happy to blue tooth to you mobile then the Fujitsu Siemens Look series may be for you. I am very happy with my N560 (wifi, gps and blutooth.) Available on e-bay for aprox £230 (retail at £330+.)