I have an HTC MyTouch 4G that I use over a wifi connection in combination with textPlus to make it into a sort of house phone. The phone used to belong to a friend of mine but has never had a carrier since it was given to me when my friend got a new phone.
Any solution involve rooting isn't a problem. Although because of a lack of SD card, I have only been able to unlock it and plan on rooting it once I buy one. But it'd be nice to know how at least until then.
It has Go Launcher on it now and uses the weather live wallpaper. This is actually why I'd like to remove the big "No Signal" message. It might seem like a stupid reason for it, but I want to make my phone look nice.