You cannot currently get access to this information via a public api. Apple provides some sample code for checking if there is an internet connection and if the device is on wifi/cellular amongst other things. This is available at:
https://developer.apple.com/library/ios/samplecode/Reachability/Introduction/Intro.html
You could also try something really hacky like taking a screenshot and doing some image analysis on the top left corner of the screen to determine how many bars there are, if you're really keen..?