I have a girl I like who likes me back but we don't get much time to talk when we in at school (both of us are under 18). She doesn't have a phone and thus rarely gets to talk with me after school. I was thinking that if I learned how, I could build a device that would allow us to send text messages back and forth for free and do nothing more. I am willing to build one and I am kinda a math genius. I would also like it to be solar powered. I have scoured the internet and have found nothing. I ask for either a relatively (or just flat out everything) explanitory way that I can accomplish this, or a set in case somebody already did this and is will to sell (but not to pricey).
Any help is greatly appreciated.