If mySMS isn't quite what you're looking for, perhaps try sending unlimited texts for free with Text free. This app has a lot to offer, and will actually let you create a phone number for free calls and texts, even from a tablet.
With Text Free you create an account and choose your own phone number. Once you have a number you can call and text anyone for free, even if they don't have the app.
Enjoy free SMS messages, picture MMS messages, group texts, international texts and calls, and even voicemail. Pretty powerful, right? All of this is free too. However, the free calls are only to other text free users. Otherwise, you'll pay a very small fee.
This basically allows you to turn any device into a phone, including tablets. It's a popular app for a reason, so give it a try today. Keep in mind it doesn't have as many theme and customization options as some. It's all about what you can do, not how it looks.