We want to create 66 assistants, each with its own number. We’d like to ask about concurrency — does it mean that if we have 66 assistants and 10 are included (so 66 − 10 = 56 active), we have 56 concurrent instances and we have to pay 56 * 10 $ line per month? Or does concurrency mean having all 66 calls happening at the same time? We need this information as soon as possible.

If you are running only one call per phone number for each of your 66 assistants and you have 56 concurrent lines paid (including the 10 free), then you are correct. It would total to $560 per month for just the concurrent lines. Alternatively, if you have only 6 assistants and you have 11 calls running at once for each assistant, same deal. 66 concurrent lines is just the amount of calls running at the same time on one account