Terminate half the wires to one jack and half to the other.
You shouldn't even need to do that. I set up a simple patch panel of female ethernet connectors in my wiring closet, each connected to the female ethernet connectors all over the house. My POTS line comes into that wiring closet (well, my DSL line does, and my box has an RJ11 POTS connector). Plug the phone's RJ11 into the RJ45 where you want the telephone (yes, male RJ11 plugs into female RJ45 by design), find a male-male RJ11 to connect the corresponding patch panel RJ45 to the RJ11 POTS line, and bingo you can have your POTS telephone wherever you thought to place an ethernet outlet.
You probably want to avoid messing up connections between ethernet and POTS though. I've done it without ill effects, but no one phoned me during the time it was misplugged.
Now that I've wasted the mod point I awarded here before posting, some other tips, not all cool new tech:
- some place with ethernet that you can have a noisy server. Servers aren't that noisy any more, but I've had to junk one supposedly silent server because the power unit emitted a very annoying high-pitched whine, and cheap hard disks still make noise. This could be the wiring closet, but not necessarily.
- there's a (maybe European) quality of cable called "grade 3" that is better than cat6 (cat6e?) in that you can wire a satellite (coax) signal directly to it.
- if you use contractors, watch them. Every day. Get them used to the idea that they can ask you things. I put double RJ45 outlets in a lot of places, but the only place I really wanted two was where I was putting the television. Guess where the cabling guy decided on his own to only put a single because the patch panel had one hole less than needed?
- if you use contractors, watch them even more than that. I have a friend who used to change out of business work clothes into worker's coveralls in order to walk around his future house every evening. One evening he sees something bad (ISTR isolation) and calls it to the attention of the guy working nearby. The reply was "Oh yeah I know I messed up but it's too much work to correct, it'll be covered by drywall, the owner will never know".
- why not run cable to the fridge? To somewhere you might want a (PoE) surveillance camera? Wifi repeater?
- battery-powered doorbells suck.
- easily accessible storage space for things like vacuum cleaner, mop, dry food, clothes
- BTW, central vacuum cleaning, but storage is good anyway.
- I put washing and drying machines on the bedroom floor instead of basement or kitchen. No more carrying dirty clothing up and down stairs, but YMMV if your sleep patterns might clash with the noise. BTW, drying machines are better and cheaper if they have a hole to the outside.
- depending on your local weather, DFV (double-flow ventilation) with heat exchange so you don't lose heat, and cheaper electricity and heating mentioned by others
- Kitchen: granite desktop. Draw-out trash can just underneath so you can just sweep peelings from the working area directly into the trash can. Dishwasher a foot or two above the usual level so you don't have to bend (you put your hand in the dishwasher a lot more often than in the oven, and kids can fall on the upwards-pointing knives in a dishwasher just like they can burn their hands on an oven). Power plugs for kitchen appliances of course, maybe ethernet?
- going to have animals? Where are you putting their food, will you shut up the dog during the night and if so where, do you need a cat door, etc.
Lots more of course, I have often heard that that the house you get perfect is the third one you build!