I got tired of putting my phone in the cupholder, and having to mess with the power cable running under the armrest to one of the two power sockets there. There are two 12V power outlets under the armrest console, and I wanted my phone in the armrest console, so....
Flip up the armrest.
Locate the points on the left & right of the underside of the armrest as shown, and go exactly three-quarter inch UP and three-quarter inch IN. it helps to make a template rather than using a ruler for this, so you can get exactly the right spots.
Take a 5/8" wood bit, and set the centre point on the spot that you marked. Note that this will give you just enough clearance between the hole that the bit will make and the support of the console. Not only that, but there is stuff on the INSIDE of the armrest compartment that you need to miss, so get the measurements right!.
Drill the two holes. There is an inner and outer layer to the console, you have to go through both.
I got rubber grommets that fit into a 5/8" hole and installed on the inside of the console (inner layer of plastic). This keeps the power cables from slipping, prevents chafing of the wire, and is just a nice finishing touch. You can get them at Home Depot (wiring section) or other hardware stores.
Pass the power cable (or iPod cable, or whatever you want) through the hole/grommet, and you're done.
If you don't want the cable there sometimes, a piece of leather (available for under $10.00 at craft stores) makes a nice liner that covers the holes from the inside. Also, you can fold the piece of leather and it'll keep the phone from sliding down under the hinge of the armrest cover. I added the double-row white stitching with a sewing machine and some heavy white upholstery thread to mimic the look of the sport seats.
Piece of leather as a liner for the console:
Phone plugged in:
The same piece of leather keeping the phone from sliding:
When the armrest is down (mine is never up), you don't see the holes.