[Asterisk-biz] Trunk-to-subscriber ratios

[Forrest W. Christian]

In the process of working through a possible VoIP business plan here I've
come across a piece of information I can't seem to find.  Let me start
with the analysis I've done so far:

Back in the modem-ISP days, I had a pretty good handle on how many
incoming lines/trunks I needed for a given number of customers - usually
between 8 and 10 to 1 at the low end.  That is, I could support roughly
240 customers per Non-PRI T1.

I also know that it used to be that average usage for internet was about 4
times that of voice.  If the ratios haven't changed, it seems like a 40:1
ratio might not be out of line, understanding that peak-usage statistics
tend to bite you harder on the low end of the scale.  That said, my
back-of-a-napkin calculations indicate that each PRI T1 with 23 channels
should be able to handle ~900 subscribers, which seems like an amazingly
high number to me.

So, I ask, what ratios are others really seeing and using?  I realize that
business vs residential vs time of day changes everything.  Generally I
want to see if the ~900 subscribers per PRI is as out to lunch as it
seems, or if this is the right ratio.

-forrest