After our last suport session I tested the card for 4 days at my office with out any problem using the last setup you did , yestarday I installed the server at my client's office using just my laptop (no firewall, no swicth) and I realized that I was having the same problem than before (90% call I got busy tone), then WHY???, I think could be a card incompatible issue with the pstn lines, because my card work flawless at my office and the only factor that change is the pstn line but why my lynksis 3102 gateway work fine?. Any help would be appreciated.
you can try to add some param in your dial command, let it wait for 1 seconds or wait for dialtone, the telephone line in your customer's site might need wait a while after the FXO offhook and before asterisk send DTMF out.