how should internal telecommunications services be priced to the end user within 
the company? As a charge-back (a standard cost per person charged-back at the 
company or divisional level)?by usage or individual capabilitry?

The chargeback method that is best for you, is whichever chargeback
method your level of information will support. At the end of the day,
somebody has to pay for it!

If your systems allow you to track usage by department, then
charge-back based on the percentage of total usage that the department
represents. If the tracking allows you to monitor the charges down to
an individual, then chargeback based on the exact amount that each
individual consumes, rolled up to a department level.

If, however, your systems do not permit you to track how the
communications is occurring, who is using it, and the relative value
of each use, then the best you can do is chargeback based on the
proportion of headcount. If one group or department definitely does
not use a particular system (for example, long distance charges may
not be incurred by some groups), then be fair and only divide those
costs over the groups that do incur them.