I've never got the "SIM Card registration failed message" error message.
All I get is a little icon in the status area.

But, you didn't say you wanted to use it on the net. I can't remember if it was a plugin or if it's built in, but there's a tablet mode that allows Wi-Fi browsing without a SIM installed. Access it via the power button, if it's not in your menu then it must be a plugin.

You could try checking in your phone settings, see what you've got your "Network selection" set to. Mine's on automatic.