|There are some wireless providers too guapo|
I live out in the boonies and since it's hilly and boreal forest, it's easier to use wireless for the real rural folk (I live in town). There are some little valley's that don't get reception due to the location of the provider's wireless antennas but for the most part, anybody in the country around here who wants it, can have highspeed in their home.
It's not as good as ADSL or Cable for obvious reasons (they're wired and wireless sucks........lol) but it IS a whole lot better than satellite.
However, I get the feeling from the OP they're talking about in-house wireless which is a WLAN.
In that case, guapo is 100% correct that you need a provider to begin with. You would then deploy wireless access points throughout your building in order to provide effective coverage for all tenants. This would require an in-depth analysis of the building with regard to wireless coverage before you could map out a plan which you would use to calculate how many AP's you'd need and their locations. Then there's getting it all setup, testing, finding and fixing the dead spots (and there will be some, concrete and steel aren't conductive to good wireless coverage - not to mention interference.....etc etc etc)
From the sounds of it, you already have network cables of some sort into each apartment. If they're actual network cables that terminate to a patch panel (or panels as the case may be) in the phone or mechanical room for the building, you could use the existing setup and drop comcast and go with a competitor. This would preclude hiring a professional to help you (which would be my suggestion in this case since you don't know much about it) or making any real changes to the existing infrastructure in the building.
It would also mean not having to go with a wireless solution. I've said it before, I'll say it again, if you want a reliable network connection with maximum bandwidth and minimum lag/latency then you want a wired solution, not wireless.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.