Two interfaces, 1 ethernet, 1 vlan, to same switch?

Hi,

SG230 at work, and I know just enough about complex networking to be dangerous.

We're upgrading our phone system and I'm thrown into VLAN chaos.

in0 is my LAN and works fine connected to our Nortel (Avaya) switch. No vlan on the interface but the switch uses VLANs 2 (data) and 3 (voice); somehow it tags/untags things right so the switch and gateway can see each other (I didn't set it up if you haven't guessed). Switch is also connected to our PBX (BCM450) which hands out phone DHCP.

Now going to hosted phone so I need to remove the PBX from the equation. I have a VLAN (3) Ethernet set up on in3 and in a different subnet than the old phone network and our data network.

Can I connect the cable that is currently plugged into the PBX directly into in3? Since it's all the same vlan will the phones "see" that gateway and beyond, and vise-versa?

Or will two unaggregated cables connected to the same switch reek havoc even though one of them is using a VLAN?

Thanks,

Jeff