I think that wifi is only as secure as the hotspot you connect to, regardless of what kind of device you use. There is no option to put a cellular radio inside a Macbook Air. However, if you have an iPhone on AT&T, most plans allow you to "tether" your computer to it. I use this all the time and it works great. You can connect the phone to the computer either with wifi or bluetooth. I think you will find a similar feature on Android phones as well.