This is like one of those,"if I shoot someone will they die?" questions. It depends totally on the situation. There are so many additional questions that pop up in my head when you say this, I would never answer you.
Some more info you may want to provide is listed below:
How many users are in each location?
Which type/speed of WAN?
what speed of backbone to you want?
how many devices do you have at both sides?
Are you running a VOIP enabled switch right now that you need to transition?
which VOIP solution were you interested in looking at?
what kinds of broadcasts do you have?
are your clients DHCP?
are you using WINS/DNS?
I could go on for hours, but I have to get to work. Find an IT consultant, (not a Microsoft consultant, a network consultant) or a certified telecommunications contractor (one who's cisco and cabling certified) to help you, you may spend a little more, but it will pay off in the long run, not to mention avoid the fire marshall from shutting down your network for violating the NEC without backboards and proper grounding and bonding.