They are 8-bit PCM, used mostly in Telephony.
It appears structures and some code is at http://cpfaq.blogspot.com/2011/03/g711-audio-codec-explained.html
Also at http://www.znak.fi/user/pdonner/g711tool/
(WAV to ULW/ALW converter - http://www.znak.fi/user/pdonner/g711tool/G711Tool.zip )
Extensions I've seen are .ulw and .alw (u-Law and A-Law, respectively... the u is actually the greek mu, so it's pronounced mu-Law).
It would be nice if MediaInfo could parse these files and report sample rate, number of samples, et cetera.