Use Talkatone to make free calls and send free texts without using any cell minutes. Stop paying for cell minutes and text messages. Call and text US and Canada numbers for free. Turn your iPad or iPod touch into a phone. Make insanely cheap international calls. Make calls over 3G, 4G and wifi. Google Talk does not support MMS so you can not share pictures with your non-smartphone friends but when using the Talkatone app you can. Talkatone an app for Android and iOS enables you to do this using your Google voice number. You can still use the Google Voice app to get your phone messages and texts.
I find that the quality over wifi very good. No delay or artifacts.