Just to clarify, are the lines disconnecting calls or is a particular phone disconnecting calls? Does this happen on all phones on those 2 lines?
I would suspect a telephone before i suspected the lines in. Sounds to me like a bad hookswitch or, possibly, a bad line cord jack in the phone (the line cord jacks come loose all of the time on Panasonic phones)
I am going to go out on a limb and guess that this is just happening on one phone. Swap the phone with a known good phone. If the problem follows the phone, then the phone needs to be repaired. Send it in!

------------------
Panasonic Telephone Repair
Toshiba Telephone Repair

[This message has been edited by paul144 (edited January 12, 2005).]