how do i text using an iPhone 4 with no mobile number on wifi only?

paddlerxxx wrote:

How do I text using an iPhone 4 with no mobile number over wifi only?

You don't.

If you mean SMS texting, that's correct, you can't. SMS is a cellular carrier function. You should still be able to send iMessages to other iOS users when connected to WiFi.

paddlerxxx wrote:

I'm using it as a glorified Itouch/Ipad. you still say I can't?

Send messages with your iPhone, iPad, or iPod touch - Apple Support