Bought a used 8820, and it connects to my wireless network. But when I try to SMS somebody with the mobile network off (so I can only connect by wi-fi) I get the message: "radio is off, message cannot be sent. You will only be able to save draft." But in Manage Connections my wi-fi network is checked as "on" and shows as "green". Needless to say, Internet doesn't work, either. What's going on, and can I fix it?

Well...SMS uses your mobile network, not wifi.

That would imply that I can't SMS unless my mobile network is turned on. But on my normal phone (a Curve) if I turn off the mobile network, I can still SMS through the Wi-fi.

Which curve?
Does that curve have UMA? if so, thats how it does it.

Only T-Mobile branded BBs can use UMA. I don't recall if T-Mobile sold the 8820 - they sold the 8800...

Yeah sometimes it says UMA