A VLAN-tagged sub-interface is basically splitting a physical interface up into multiple layer-3 interfaces, with each sub-interface associated with a partiucular VLAN tag. Contrast this with an ethernet-switching interface where one or more ports can be put into the same bridge-domain (broadcast domain) identified by VLAN tag. If you are plugging in VoIP phones, etc. I would suspect you are using standard ethernet-switching interfaces. From a configuration-standpoint, they look quite different:
Routed VLAN-tagged sub-interface
-----------------------------------------------------------
ge-0/0/1 {
vlan-tagging;
unit 100 {
vlan-id 100;
family inet {
address 1.1.1.1/30;
}
}
unit 200 {
vlan-id 200;
family inet {
address 2.2.2.1/30;
}
}
unit 300 {
vlan-id 300;
family inet {
address 3.3.3.1/30;
}
}
}
Access-port for Ethernet switching
------------------------------------------------------
ge-0/0/2 {
unit 0 {
family ethernet-switching {
port-mode access;
vlan {
members data-vlan
}
}
}
}
Trunk-port for Ethernet switching
--------------------------------------------------
ge-0/0/3 {
unit 0 {
family ethernet-switching {
port-mode trunk;
vlan {
members [ voice-vlan data-vlan];
}
}
}
}