Peter-

We don't have the KX-TDA30 here in the US yet (if it’s coming), but I'm doing the same scenario right now only with a KX-TDA100 and am using the 4 channel gateway card KX-TDA0484 and for the KX-TDA50 I'm using the 4 channel gateway card KX-TDA5480 along with two of the KX-TDA0920's one in each system. Regarding the gateway cards, since you have a KX-TDA30 and a KX-TDA3480 gateway card and the KX-TDA50 uses a KX-TDA5480 gateway card I’d say that is your card.

I'm having some issues with my VPN tunneling so mine doesn't work yet, but I know I had to upgrade to version 3.0 on both systems however, another tech who works with me said the TDA50 wouldn't take the KX-TDA0920 sd card. Again we haven't got the system's talking yet and I haven't tried to put the files on the sd myself yet. My point is your TDA30's may not need the sd cards? But I can't say that for myself. I'll post as soon as I have a definite answer (tomorrow or Monday).