I have been told by my salesrep at Graybar that the standard nowadays is to use T568A for phone connections with Cat-3. I scoff at that, and use USOC for Cat-3. However, just like scs says above, using 568A or T568B will work with phones, which use either one pair, or in rare cases, two pairs.

However, since 568B will work the same (and the only difference is color), I use 568B on all Cat-5 cables. One really good reason to follow the color standard for pairs is that you can crimp one end and punch down the other end to a modular jack, such as when cabling an office or house. This way, you have crimp ends on all of the cables in the wiring closet, and modular plugs at all of the stations. Another great reason is that you can re-crimp one end without having to examine the other end.

I have found that Allen Tel Cat-5e patch cables do not follow the pair color standard, and use random colors, while still conforming to the pairing rules. This is probably true of other brands.

Another thing to note is that you can purchase crimp ends which are designed to work with stranded conductor cable in addition to solid conductor. These have a smoky appearance, rather than the clear plastic of the ends designed for solid conductor only. The difference is the shape of the 'teeth' that bite into the wire.