If you're talking about 2 phones at one jack, simply make or purchase an L1 + L2 +(L1+L2) from Graybar or similar supply house.
For only 2 phones from one jack...
If the jack is wired USOC the field pairs should be blue and orange pairs at the demarc end
If it's a 568B "wired jack" on the field side, then the demarc side pairs would be blue and green
If it's a 568A "wired jack" on the field side, then the demarc side pairs would be blue and orange
It's possible some Radio Shacks would also have an (L1 + L2 + (L1+L2)) (you won't use the L1+L2 jack, only L1 and L2 on this device)
Your station pairs would simply be connected to the appropriate field pair. (this may sound more complicated that it really is)
The "more correct" way to do this is to replace the plate with the necessary jacks, but this (the adapter/splitter) will most certainly work and doesn't necessarily require a NEC certified tech - Just be sure you know where the digital or analog jacks are located on the NEC side - depending on the wiring, you might need 4 bridging clips if split 66 blocks are involved - just "go easy" and think "it" through
If you need help though, at least consider contacting someone with phone experience - this is a relatively minor matter for someone familiar with our world (easily doable for a person with an reasonable level of logic)
