Using Asterisk to test is phone line is dead

I have asterisk 1.4.17 and Zaptel 1.4.7 using a TDM400 with 4 FXO cards.

Being the rainy season in Silicon Valley, rain is getting into the phone lines in this third world country right next to Google. So lines are going dead all over the place.

I use the Group Zaptel setting which will look for an unused line before dialing out. However if the line is dead, the Zaptel driver still tries to use that line.

I can set up an extension where the user can dial it and then dial a number to get to a dedicated Zaptel channel. Then the user can see if he gets out.

Is there an method in which the zaptel can check to see if it gets a dial tone within the asterisk dial plan?