Where to start

Before you start adding new routes to your customer's Asterisk system you should, of course, sit down and take stock of what your customer's call profile is like at the moment. How many calls are made in a typical month? How many of them are local, national, international? What are the destinations of the international calls (and the national calls too if this makes a difference to the call cost)? What hours of the day, and days of the week, experience the call volume peaks and troughs? How long does the typical local call, national call, and international call last for? In other words, you need to understand what is happening to the calls within your company, or your customer's company if you are a consultant.

You should also try to gain an understanding of the costs and options available to you from telephony suppliers. For instance, at the time of writing, a major telephony provider was offering the following call package to small businesses with an annual spend of over $500:

Of course these are headline figures and don't show such items as the per-minute rate to mobiles/cells or any international call charges. There is also a line rental charge to factor into the equation. However, these figures do give a flavor of the type of deal that is available. When carrying out this exercise for real you should, of course, see what deals are available from a number of suppliers.

Taking the example above, we can see that a customer that makes lots of local or national calls with an average duration of 40 minutes might very well spend less than a customer of an ITSP who offers such calls on a flat rate of 1c per minute. In fact, until recently, it hasn't been unusual for the cost comparison between PSTN and VoIP providers for local or national calls to come down in favor of the PSTN provider, a fact recognized by VoIP providers who now offer similar bundles of calls at low prices in an attempt to grab a share of that particular market sector. Offers of unlimited national and international calls (to a restricted list of countries) for about $20 per month can currently be found.

When carrying out these exercises, there is always a temptation to get drawn into a "what if" discussion. "What if" the company doubles in size over the next three years. "What if" the company's customers prefer calls to mobiles more and more. In truth, there are any number of "what if" questions. However, it is difficult to make an informed decision when enough detail is not known. Bear in mind that altering the profile of your call routes in Asterisk is not an onerous task, so changing circumstances can be catered for as they occur.

Thus, by now you should have a good idea of how many calls the company makes, the main destinations and the times of the day, or night, at which they are made. With this information you can decide what external routes you need to consider. Usually they will be a combination of the following: