As has been pointed out many times before unless your dialler is certified for use on a public telephone network then connecting it and using it on that network is completely illegal.The reason it is illegal is prcisly because if it hasnt been designed properly then nobody knows what it is doing to the network and what damage you are doing to the local exchange.
If it is certified for use on the public network then it shouldnt be intermittant in its working,so I don't know what the problem is unless you have destroyed the switch