Be very careful how you crimp the wires without the use of a proper crimper. While you can buy a plastic crimper for about $7 at a lot of dollar stores, they just don't give that extra little "crimp" which you can feel at the last second when you use a good crimper.
A good crimper will cost in the range of $25 - $35 and is well worth the investment if you are going to be making a number of cables. Or, if you belong to a MR club with DCC (like I am), you can become the expert in LocoNet, NCE, or whatever other telephone cabling system you use. Check the bottom of this page on my website.
http://www.railwaybob.com/Modules/WiringRJ12s/RJ12s01a.html
The standard you want to use is RJ12 6-wire cable (RJ11 is only 4-wire cable). The terminology is not standardized so you want to make sure you get the 6-wire cable. For those of you who use Digitrax, here are the wiring standards.
http://www.railwaybob.com/Modules/WiringRJ12s/RJ12s01.html
A word of caution. If you are using female RJ12 telco jacks, some of them are disguised as RJ45 jacks. That is, the cover has the proper width of 0.383". However, the interior of the jack has a width of 0.463". There are also blank slots on each side which can accept an extra pin (for a total of 8-wires instead of 6). If you use this type of female jack, your RJ12 plug could get stuck in the jack, short out some wires, and cause you some grief. I've bought RJ12 telco jacks from Home Depot that were really RJ45 plugs disguised as RJ12s. However, all is not lost. Here is a description of what they look like and how you can modify them into RJ12s.
http://www.railwaybob.com/Modules/WiringRJ12s/RJ12s01a.html
If you look carefully at the end of a crimped RJ12 plug, you will notice that there are small plastic ridges between the contacts. This is where a good crimper comes into play. It crimps the brass contacts firmly into the notches between the plastic ridges. At the same time, the "knife" part of the brass contact slices through the insulation on the wires and makes contact with the wires. It's this part of the crimp that a plastic crimper falls down on the job. My experience with a plastic crimper was one of hit and miss. I can't even give it away.
There are two other parts to a crimper which are also very important. The first part is the "guillotine which "slices" the wire nice, square, and clean. Don't use a pair of wire cutters as wire cutters will squeeze the ends of the wires.
The second part is the two blades which "nicks" the grey, white, or black plastic cover and removes just the right amount of cover to expose the 6-wires below. The length of this plastic cover that is removed is most important. You might try to do it with a utility knife but you risk the chance of cutting into the insulation of the wires below, or, the amount of cover removed is either too short or too long.
So, if you are going to be installing a fair bit of 6-wire RJ12 telephone cable, why not invest in the proper tools to do the job correctly? I only intended to make about a dozen or so crimps. So far, I'm over 200 crimps that I've made either for myself, for club members, or for friends.
Bob M.