I'm using my iPad Mini as a phone. I use Line2 App. http://www.line2.com/home/
Really great. $10/month Here is what I get
Ideal if you only need Line2 and its standard calling features
- Tri-mode (Wi-Fi, 3G Data, or Cellular) calling on your phone with one number
- Turn an iPad, iPod Touch, or Android tablet into a Wi-Fi mobile phone
- Unlimited US/Canada calling and texting with any device on any carrier
- Low rates for international calling and 10c per international text
- Advanced call handling features like call waiting, hold, and transfer
- Conferencing for up to 20 people right on your Apple iOS or Android device
- Multi-tasking support for iOS4 and Android – receive calls and texts even when using other apps
- Visual voicemail with voicemail by email
- Call screening with automated caller announce feature
I use the magicJack app on my iphone. It is only $30 a year (you don't have to buy the actual jack, just download the app, create an account and "renew" membership). I have a local Canadian number and it works over wifi or data. It is great if you are travelling to other countries and you buy a local "pay as you go" SIM card with your unlocked iphone. I forward my work phone to my local magicJack number and leave my work phone behind when I travel. That saves my company $100 in roaming package add ons and roaming data/talk rates.
I have a T-Mobile SIM card for traveling in the US ($3 a day unlimited everything pas as you go).
The app will work on ipads as well, but it is formatted for an iphone sreen. It does not look as fancy as the Line2 app mentioned above, but if it is all you need, then save he money