how do i connect my iphone 4 to talk talk wifi?

to talk talk wifi? Or do you mean use iMessage or facetime through wifi?

What does the provider's web site say?

Telephones do not talk over WiFi, except using certain specific applications such as Skype.

If you plan to talk on your iPhone used as a telephone, it will go through your cellular carrier's voice process.

The OP is refering to Talktalk telecom, a British ISP: http://www.talktalkgroup.com/

Ah, OK, blissful ignorance on my part.

Thanks.

Fooled me too, initially. Until I DDG'd it.