Text goes over 2G, so no phone can send it over wifi. It's like asking what kind of wire you can send gasoline through, silver or copper. There are email-to-text gateways that you can use on wifi to send an email to the gateway, that the gateway will send to the recipient as text. (Some of them will even return, so the recipient's text to the gateway gets turned into an email to you.) Do a Google search for email to text gateway.