[For some reason this was sitting in my draft folder, never published. I wrote this post about 5 months ago.]
If you are starting up a business, or just expanding and are moving into a new location you are going to have lots of things to consider. This is the best time to do some forward thinking.
If you are doing new construction you should consider getting the low voltage tech on site to do a survey early. So many times I have gone out to a job to wire everything up after the construction is completed, or too far along, and have to make holes into newly installed and/or painted sheetrock.
Have your data and telephone wiring run to the same closet. Use at least CAT5 for your phone jacks, as well as data jacks. Every desk location should have at least 2 jacks - either 2 CAT5 jacks (if you are going to be using VoIP phones) or 1 phone jack and 1 data jack. The reason that you are going to want your phone jacks run with a minimum of CAT 5 wiring is that in the future if you decide to move over to VoIP, you will be able to convert your phone jacks to data jacks, and keep your VoIP phones, and computers on two physically separate networks. While most VoIP phones have dual ethernet jacks (one to connect to the network and another to connect your computer) it is best if they are connected to two separate networks. This will eliminate troubles further down the road, and reduce disruption if one network needs to be worked later on.
The reason that you want to bring your phone and network cables to the same location is for future changes and upgrades. If your phone and data networks are at two different locations then you will likely need to pull new cables between these two locations in the future. If you have no choice but to locate your phone and data networks in two separate locations I would recommend pulling several cables between the two locations.
Pull a cable from your communications closet to the main demarc from the telephone company. Pull at least a 25 pair cable. Also pull an RG6 from your communications closet to where the cable comes to the building.
Don't forget all of the extras aside from your computers and telephones. Consider what doors are going to need to be wired for door phones, and door releases. Are you going to need an overhead paging system? Do you need to pull additional wiring for wireless access points? How about CCTV, where do you want to place your cameras? What about additional monitors? While you are at it, consider your conference room. You are probably going to want data/phone jacks and electric under your conference table. What about video presence? Do you want to install hardware for video conferencing, or perhaps want to pre-wire for a future addition of video conferencing? How about an overhead projector?