I'm actually not sure of your question because of the lack of details. Examples:
Reasoning?
Are there 2 line phones in the house?
How many phones?
DSL part of plan or future plan?
Are there any L1, L2 and L1+L2 adapters in the house.
1) Both lines are run to all jacks and they are separated by a small adapter that says: Line 1, Line2 and Line 1 + Line 2.
2) Separarate lines from the NID (Box outside) were run to one or more locations as Line #1.
What does that mean?
Take a phone and it's cable and plug it in the test connector at the NID. Remove the jumper first. That test connector will only respond to line 1.
Take that phone and see if you get dial tone on all the lines.
Then disconnect one line at the NID and do the same. Now do the other. Call the oposite number to identify the lines.
From this information, you will know:
1. What phone number is line 1 at each of the jacks.
If you get the adapter, you can determine if line 1 and line 2 are active.
Radio Shack sells a very inexpensive little two line tester, with a couple of lights on it.
If a line is active it glows one color, if it has reversed polarity it's the other.
A map of location, Line 1 number, line 2 number would be essential information and you can determine that very easily.
1. Disconnect the test jumper in the NID for the blue/white line.
2. Use a phone plugged into that line to call the other number.
Busy - your number or someone is tring that number too. Ringing - the other number
2a. Say your testing Line 1 and it's blue/wht
3. Make a sheet with room, Line 1, Line 2
4. Take the tester and note the line that's blue white
5. Disconnect the other side and plug the first conncter back in
6. Do the same
get a list like:
blue/wht pair = 555-1111, P1 (pair 1)
Orange/wht pair = 555-2222, P2 (Pair 2)
Room L1 L2
F BR 1 2R
L RM 1 X
Kit 2R 1
Den 2 1
Porch 1 X
In that table, I've identified which number is pair 1 and Pair 2 in each room, an X if they are not connected and an R if reverse polarity. From that information and the pair that's being removed, you can consider your options.
Line 1 refers to the telephone connected to the 2 center conductors of the telephone cable. Line 2 refers to the next outer set. Line 1 may not be the main telephone number.
The blue/white pair in the NID is USUALLY the main line or pair #1.
Telephone Line and Wire Troubleshooting from the Natural Handyman Home Repair and Do it Yourself website