Hey, I've got a question regarding this particular switch.

I am trying to get part of my network configured and the only thing I have left is this switch. On it I have multiple VLANs but for the sake of simplicity and my problem, I have our user subnet as let's say VLAN A, default/mgmt port VLAN as B, and voice VLAN as C. On the ports with phones, I have VOIP phones, and tethered off of those, I have user computers. I am trying to get the computers do have VLAN A, and the way to do that is to set the native VLAN on that specific port to be A, while also tagging VLAN C on that port. Only problem is, every time I plug in the computer off of the phone, the cisco switch AUTOMATICALLY changes the interface to VLAN B (the default VLAN). My question is, how can I exclude certain interfaces from defaulting to the default VLAN? Surely this can be done, and I need that default VLAN for management, so I can't the default vlan to be the same as the computer VLAN (primarily because I also need to tag the computer VLAN on the uplink port, and changing the uplink interface from untagged to tagged will not work).

Any help in this regard would be very much appreciated, and thank you.