Probably somewhere in their specs, tho I don't recall seeing it.
The failure rate (in actuality) seems reasonable/comparable to other systems. I have approx 2500 phones in service since July 2010 and in that time I think we've lost probably about a dozen, mostly out of warranty. Calculating the numbers that works out to approx. 3,650,000 hours mtbf. When one does crap out we toss 'em in the recycle bin. Too much hassle to send out for repair. (company politics)
I also have 12 of the 7975 model in constant heavy 24/7/365 use and have not had a moment's trouble with those, so I'm inclined to think failures aren't so much based on wear as they are just Murphy's Law.
New out of box failures (infant mortality) in the whole order was zero. Of the failures that did occur, most happened past the 12 month warranty period. One guy spilled coffee on his, can't blame the equipment for that.
Original MUG/NAMU Charter Member