Before Voice over IP, there was callback

A recent post by Julian Bleecker on how people will devise complicated systems to find a way to communicate reminded me of the time I worked in a callback company.

In areas where owning a cell phone is not routine — for economic reasons, predominantly — it is not uncommon for a stranger to ask another stranger to borrow their handset to make a call. This happened to Francois on a trip somewhere and he, being a nice guy, agreed and handed over his phone. Only he thought this stranger was going to just go ahead and make a call. Instead the stranger dismantled Francois’ phone — removed the back, spilled the battery out and popped out the SIM card and then popped his own SIM card in there, reassembled the phone and made a bunch of calls in rapid succession, hanging up on each one after the first ring or two. (Mobile Phone Usage Idiom — No. 1)

While I worked there, I experienced a lot of so called hacks both to prevent callback to operate and to fight these restrictions. I had to designed some of these hacks to keep the service operating in some countries. Let’s first explain how callback works.
Callback is based on the following principle: instead on making one call, make 3 calls with the help of a distant machine. On the downside, calling somebody can be seen as a hassle but on the plus side, you can make calls for much more cheaper (depending on where you are located).

How does callback works (the original system)

  1. You contact a callback company
  2. They create a account for you with the following information
    1. the number you need to call, which is uniquely assigned to you
    2. the number where you want to make the call from
  3. You call the number assigned to you
  4. You let it ring (generally once is enough)
  5. You hang up before anybody picks up
  6. The company (which recognized you based on the number you called) calls you back
  7. You answer the call and get a prompt to dial your destination number
  8. The company puts you “in relation” with this number
  9. Once you hang up, the company will have billed you for 2 calls: once for the call from the company to you and once for the call from the company to your destination number

An example of how it works

Person A lives in Angola and wants to call Person B who lives in France. This kind of call are usually really expensive (more than $1/min). Person A decides to signup with a callback company (like United World Telecom the one I worked for). Person A account main information would look something like that

  • Callback Number: +1 305 555 1234
  • Source Number : +244 123 456 789

Now Person A wants to call Person B whose number is + 33 9 12 34 56 78. Person A will need to do the following:

  1. Person A calls the number +1 305 555 1234, let it rings once and hang up (cost = none)
  2. The company receives the call on a group of lines dedicated to receiving these call ( like 10-15 lines dedicated and matched to hundreds or thousands of phone numbers). The phone number +1 305 555 1234 can be thought of as being a “virtual” phone number, there is actually no physical line dedicated to this particular number. Along with the call, the telecom operators along the way are passing along the phone number in a format that can be captured by the callback company.
  3. Once the phone number is captured, the callback company will look up in its database for the phone number called (here 305 555 1234)
  4. The callback number is associated to the corresponding source number
  5. The callback system picks up a line, calls the number +244 123 456 789 and wait for the person to pick up
  6. The callback system picks up another line, calls the number +33 9 12 34 56 78 and link the two lines on its system so that Person A and Person B can talk to each other.
  7. Once the call is finished, Person A can end the distant part of the call with a key combination and redial another number or hang up
  8. On the callback company side, the two calls are added up and charged to Person A

Cost (as of 2002)

Option A: Direct Call from Angola to France: > $1

Option B : Same Call using callback

  • Trigger call: Free
  • Call from US to Angola: approx. $0.40/ min
  • Call from US to France : approx $0.05/min
  • Total: $0.45

Next, I will describe some of the features (speed dials,…) and how they can sometimes serve other really important functions that the ones they were originally designed for.