Layer 1 going down for T1 line is not a good sign. So looks like the T1 is flapping and calls are failing.
first make sure that T1 remains up which you can varify using "sh controller T1" it should reports no errors etc.
Now after that make sure that ISDN signalling on layer 2 is happy using "sh isdn status" Layer 2 should be "MULTIPLE_FRAME_ESTABLISHED"
Now turn on
debug isdn q931
debug spe modem trace all
debug csm modem
term mon
To know what is going on when you dialout using atdt