Microsoft has replaced Windows Mobile, the operating system your iPaq uses, with Windows Phone. Thus, outside of third-world countries, your only option is to shop for an old model on Ebay or the like if you want to stay with the same platform/interface you're used to. Nearly all come with built-in WiFi, though, so you're free to take your pick.
I have an HP IPAC 2790. I love the Microsoft interface. Don't want to go to Apple. My unit is dying, out of touch, etc. Is there a unit out there that does similar things as an IPOD touch but one that uses Microsoft platform and interfaces with WIFI but one that I don't need to pay for service?