Since inbound calls to your toll-free numbers are charged on a per-minute basis, they do not count as a concurrent call for your trunks. In other words, if you have two trunks and have 5 inbound calls on your toll-free number at the same time, you are still not using any of your unlimited trunks, so you can still make or receive two normal calls.
Visit http://www.sangoma.com/legal to view the current SIPStation terms of service.
How to Obtain a New Toll-Free Number
Please see our wiki Adding Services or DIDs to Your Existing Account for instructions on selecting and purchasing new toll-free numbers in the SIPStation Store.