Server co-location questions and bandwidth requirements.

Well,
I am very new to the concept of server co-location but it seems like a cost effective solution for attaching ones servers and or network equipment to some heavy duty bandwidth with out having to invest the large sums of cash required to pull in dedicated lines (aka T-1, T-3, etc.) to your own location. It actually seems like a more cost effective solution considering most co-lo datacenters also take care of security (secured locations with CC surveillance, armed guards, etc.), electricity (UPS, diesel back-up generators, etc.), etc. anyways, I am considering co-locating a 4U server just to mess around with and develop an asterisk telephony infrastructure for coordinating and facilitating VoIP communications. I am actually hoping to use my server to centralize my telephony operations using Asterisk. Now that you know what I will be using the server for I was wondering if you could clarify some things about co-location for me. First, is bandwidth, I have been digging around the web and have found different services advertising different connections. For example, some advertise 10 or even 100mbps un-metered, while others offer say, 3,300Gigs of transfers a month, 20mbps burstable to 100mbps with 3,300Gigs of transfers a month, 1 Mbps Bandwidth, Equivalent to 330GIGs, or 5mbps dedicated. What does all this mean; it seems a bit confusing as to what I actually will get with each of these options. As you might be able to tell, I am a little frustrated and confused as to how the concept of bandwidth works at a co-lo. I understand the 95th percentile system just for the record. Anyways, I would just like some advice. What type of bandwidth would I need for my application? What are the differences between types of bandwidth (un-metered vs. dedicated vs. the rest)? How much bandwidth would I need? What should I keep an eye out for (any specific bandwidth providers)? Any help would be appreciated.

General specifics of asterisk server work load:
My asterisk server must be able to terminate and originate calls to and from my endpoints (using SIP) as well as my VoIP provider’s trunk (using IAX2). I expect a call load of 20 or so calls at any given moment using the G.711 codec.

At this point price is not an option as I am just putting out feelers to try to get an idea of what I actually need as far as bandwidth goes considering my current workload.

Sincerely,
Slice

P.S. I am in the greater Los Angeles area so I would prefer a co-lo within a few hours drive so I can perform hardware maintenance if necessary. Could you provide any suggestions as to some good providers in my general vicinity? Any co-los that I should stay away from?

Also Note: For those who are not familiar with VoIP each call using the G.711 codec requires ~87kbps of bandwidth in each direction, lets just say 100kbps to be safe, therefore requiring 100kbps up and 100kbps down to sustain a single conversation.

Slice

P.S. When speaking in co-lo language, is the advertised bandwidth full duplex or half duplex? For example, is a line that is advertised as 5mbps really only 2.5mbps in each direction or a full 5mbps in each direction?