There are many ways that your voip service can affect your guild culture. You have complete control over this, believe it or not. Your voip service (either teamspeak or vent, generally. I don't know anyone that uses the in game voip client) is the place where your guild members really get to know each other, where friendships are made, tempers flare, fights and love affairs occur. It is where you all come together to raid, and often where people choose to hang out when gaming in other games to WoW as well.
As a guild leader, you can really influence the way your guild glues together with the way you set up your channels in vent (I am going to use the term vent l from now on, because it is the server I use. Feel free to substitute your server in wherever I use the term vent).
First of all, I would actively encourage everyone to be using some kind of vent in their guild. One of the real basics of good raiding is a good guild friendships, and one of the fastest ways to build friendships is by talking to one and other. Welcome new members into vent as soon as you can. But more on that later. First, the dos and don'ts of creating vent channels.
Keep channels to a minimum.
The more channels you have, the more fragmented groups of people can be. You want your team to coalesce as a whole, giving the team opportunity to segment into cliques is not necessarily something you want to encourage. That said, you probably want to have channels for different purposes: arena teams, 10man teams, battleground teams etc. Having multiple channels with a purpose is fine, because you are imposing a reason upon being in those channels.
Having social channels is also a very good idea. Letting people know there is a place to chill and chat is encouraging of team building. Jus be wary not to have too many social channels.
You will probably need an officers channel. Sometimes you need to deal with guild matters that are of a sensitive nature. For example, how trials are going, dealing with guild drama, setting up the raiding teams for the night. This should not be done in front of everyone in the guild unless you have a very special type of guild or you are fostering a very specific type of guild culture. Talking about sensitive guild topics brings me to...
There are some very good reasons to password channels. The first one that comes to mind is simply the server password to stop non guild members coming into your vent server and grieving your guild. That one is a no brainer.
The next clear candidate is the officers' channel. Putting a password on this is probably a wise idea. The last thing you need while discussing a sensitive guild drama issue is the person you are talking about to come barging in and hearing what is going on. Why cause more trouble than is going on in the guild already?
It starts getting murky after this.
The next thing I would recommend is divining your vent space up into public and guild members only sections. In the public area, create sections for pugs run by your guild members, pvp, raids, anything. Personally, I had a policy that as long as a guild member was in the channel, they could bring anyone they liked in. This allowed guild members to spontaneously create pug raids, do pvp with friends in other guilds, that kind of thing.
In the guild members only section - password the root of the tree and make sure your guild members know it. Put your main raiding channels in there and keep onto of enforcing the guild members only rule.
I would never password channels as that creates segregation of the guild base. For example, never let guild members create channels and password them. What happens is that cliques form. Once cliques start forming they start excluding people within a team where you are trying to promote wholeness and harmony to create a solid team.
I can probably pinpoint exactly who and what caused the first fractures in the raiding team in my old guild. There was a member who actively promoted his 10mans and ran them in passworded channels that were not handed out to the guild. Those people then sat in these channels socially as well. The 25man team was then split into 3 groups - the officers and close friends, this group and the rest of us. Slowly, the rest of us are quitting as we are left out of the "good" groups for everything. Why would we stay when things are lonely and not fun? But I digress.
Phantoms and binds
Phantom is a function that allows people in other channels to eaves drop on conversations in channels they are not in. Binds are like push to talk keys that allow the user to transmit only to configured receivers. Allowing these two functions on your server again creates segregation in your team. The worst use I have seen of binds is within a raid group, during raids, people taking the piss out of other raid and someone accidentally didn't bind and the whole raid heard. The other bad example is the officers talking in binds, leaving the raid wondering what was going on with no direction. Binds are something I find to be worse than passworded channels, as they are user configurable and usable during times when you want people to be working together.
So, what does this all mean?
The tl;dr version of all this is that you, as the guild leader, have a lot of control over your guild culture in ways you perhaps don't even realize. You have control over HOW your guild interacts with each other. This is true for other mediums like web pages as well, but I will talk about that in another post. How you set up your vent server, how you let your guild members use it will directly affect how your guild morale progresses, and you had better be prepared for that and set your vent up in accordance with the way you want your guild to function! Better to be in your control than to inadvertently contribute to your guilds demise in these times of stress.