Peter-

I've got it done. I used linksys wrv54g's for my VPN tunnels. Which worked great once in the field, not so well on the bench.

In a kx-tda 100, I installed a kx-tda0484 which gave me my 4 call gateway paths, as well as a kx-tda0920 network sd card.

In a kx-tda 50, I installed a kx-tda5484 which gave me my 4 call gateway paths back to the kx-tda 100, as well as a kx-tda5920 network sd card.

In your case you would need those items I mentioned with the kx-tda 100 above. With the kx-tda 30 (even though I'm only assuming, since we don't have here) I would think you'll need a kx-tda3484 for the voip gateway, as well as a kx-tda3920 network sd card.

Good luck. Post if you need help.