Random? busy signals on outbound analog calls

We set up an asterisk@home server for our office using a Digium TDM wildcard (4 FXO ports) to connect to the PSTN and SIP phones and a T1 line for each extension.

Incoming calls work well as do internal calls to extensions. Outgoing calls, however, every other time (at least) return a busy signal. We had the phone company come out and check the lines (they claim they are fine and I don’t have any problem dialing out with an analog phone without Asterisk) and we had an asterisk consultant come in and look at asterisk and everything appears fine there (we can see it dialing the ZAP channel; it thinks its made the call just fine).

Is it possible that either the card is defective or that the drivers aren’t installed right (they were prepackaged in Asterisk@home)? I notice that when I run zttool, it’ll tell me there are active channels even when there are no incoming/outgoing calls?

We’ve been trying for two weeks to figure this out (I’m not an asterisk programmer; just the person who got stuck implementing this) and I’m pretty clueless at this point, so any advice would be appreciated.