I've just downloaded an app from the App Store called System Status which gives you detailed information about the iPhone it's installed on.
One of the features provides a system log which allows you to see the network info when you roam from one BSSID to another.
My question is how did they do this?
I have searched everywhere and the only way I have found requires the use of private APIs. I am assuming that since this app is live on the App Store there is a legal way to obtain the information.
After some deeper digging I think that they got the information from the Apple Status Log, more details are available via these links:
https://developer.apple.com/library/ios/#documentation/System/Conceptual/ManPages_iPhoneOS/man3/asl.3.html
http://www.cocoanetics.com/2011/03/accessing-the-ios-system-log/