I just started watching "Studio Secrets With Krish Sharma" on Groove3 and during his demonstration of miking drums he surprised me by bringing in one extra mic after the close mics, overheads and usual room mics had been set up - an old telephone handset turned into a mic. He brings it in quite close, a couple of feet from the kit at about waist height. The idea being to add a little thin, distorted sound for a bit of pizzazz. 
 
Sooo...I'm just wondering, is this a commonly used technique? 

Never heard of such, but it is certainly feasible. The Navy uses sound-powered phones for communications, and talking into a transducer will generate a voltage. I am not sure how much voltage this would create, but from a drum probably more than an instrument cable (not sure). The only other thought that comes to mind from this is the frequency range they were designed for (essentially 2-3KHz), so I would expect that "mic" to have tonal coloration; but if it works, it works. Does he isolate that signal to let you hear what it sounds like?
 
+1 for "creativity" though.

Yeah he lets you hear it as it comes in, sounds exactly how you'd expect it to sound. Just another color on the palette I guess...mix a little in for color, or even solo it for a few bars for variation and texture. Makes me wonder if I could use my iPhone's mic in a similar way, although it's bandwidth is considerably wider than a telephone's.

It is also common to use various speaker cabinets as microphones. Place around the drum set or guitar amp to get "natural" unique tones not attainable by EQ or effects. Bigger speaker cabinets have a resonant frequency that can be good in front of the kick drum. There is one company (can't remember name) that makes a transformer that connects to the speaker cabinet and provides an XLR to plug into your mic preamp. The transformer steps up the impedance to 600 ohms and gives a larger output.
Or, you can just connect the speaker straight to the mic input, pins 2 and 3, without transformer, and use more preamp gain. 

Very interesting things to try. Thanks.

I've used telephone (carbon) mics on drums in the past with some success...on the right song you may hit on the perfect weirdness.
 
My favorite odd drum mic technique is to mic a piccolo snare with a Shure bullet (hamonica style) mic from below.  Gives the greatest snare sound and no one will be able to tell how you got it.