3750 VLANs

Yes and No. You can have auxiliary VLANs configured...most often used for voip devices. What this means is, the device directly plugged into the port is on the primary vlan (say the voice vlan if this is a phone), and then whatever device is plugged into the back of the cisco phone is put onto the secondary/auxiliary vlan to keep voice/data separate.

If you are asking about a port truly being in two different vlans, that is not possible without trunking (generally ISL since dot1q is proprietary to cisco). If you trunk, you can trunk both vlans and the box will need to have logical interfaces in both (unless this is promiscuous and for a sniffer or probe, then it can just listen).

FWIW: this is done using a form of Cisco trunking..

Unlike the ancient Cisco switches, multi-vlan was dropped in all modern line of switches. Probably for good measure.

In reflection, there's not really a good reason to have ports in multi-vlan use, its not a good security model.

ISL trunking is Cisco proprietary, dot1q is a standard. Only Cisco's really old switches only support ISL, and all the recent ones only support dot1q.

Yes you are right...sorry...got mixed up for a second. Dot1q = standard, ISL = Cisco.