I'm thinking of getting a Polycom Soundpoint IP 550. From what I've read in the documentation, it doesn't have a Flash button or anything equivalent to it. For those of you using Polycom phones with your OBi, how would I initiate a 3-way call if I have no Flash button? I tried doing a quick on-hook/off-hook on my analog phone, but that wound up hanging up on my inbound call.