Advantage: You save ports in your switch
Disadvantage: You share the bandwidth on the switch port - but as the bandwidth used for IP phone traffic normally is very small, then it should not be an issue.
Thanks for your answer. This will be very helpful. Do you know any article or white paper that refers to this topic as I have to present it for a Business Case?
Another disadvantage comes in if you want go have gig to the desktop. If you already have gig switches, you have to make sure your IP phone is also gig. I had a couple of customers (working with another vendor before us) who replaced their switches from 10/100 to gig switches, but completely blanked out on the fact that their phones are 10/100 only.
A loop/broadcast storm on the data vlan will affect the bandwidth of the port and mess with the sensitive voice traffic. You can always use QoS to overcome this but the config is harder than if you use separate ports for phones and PCs.
Not sure if you can get some additional info for your presentations here:
Thanks to all of you for your comments and support. This has been quite illustrative and clarifying in order to take a decision...
Aside from the comments from others, one serious advantage for connecting the PC to the phones is the clutter of cables on the desk and on the patch room.
Because you are doing this, you don't require extra cabling.
Disadvantage - you won't get the throughput from the PC going through the phone as opposed to the PC directly into a switch port. The IP Phones don't have very powerful CPUs and I've noticed a 30% decrease in throughput going through a phone.
For normal day-to-day traffic that is probably no big deal. But for high-end systems that need to move tons of packets, fast, I'd bypass the phone.