A long time ago I was working for a "telecom" company that was using prepaid GSM cards to connect calls coming via VOIP to local Colombian numbers. (simple business model, selling US->Colombia for 10 cents a minute while we only had to pay 1 cent for the same call Colombia GSM->Colombia GSM).
US initiates call-> VOIP(free) -> Colombia GSW Gateway filled with Colombian Prepaid Cards -> Actual Colombian Number dialed by US.
In order to get that 1c per minute rate we had to activate the card by means of an IVR.
Initially we had a few dozen gorgeous naked women that would go though each card and activate it in a phone, one by one. Pretty soon it became clear that this wouldn't scale considering the sheer number of cards that needed to be activated per week so management thought that since the IT department had a lot of spare time we should help the girls out.
So this is what we did:
- placed the cards in a VOIP-GSM gateway, dial the IVR automatically using Asterisk and going through the menu by sending the corresponding DTMF code in order to activate that specific 1c/min promotion. This worked out pretty well for a while.
Our biggest concern was, and here comes the hack, we were activating the cards on the same GSM cells (antenna site) each time and the local telecom operator, reluctant to support our cause and share some of its revenue with us, had noticed the spikes in the number of card activations on those specific cells and started banning the cards from their network before we actually got the chance to use them.
Our solution was to create a telecom-SIM-activation vehicle, install a VOIP-GSM gateway with it's 32 SIM cards in a car together with a wireless modem, ironically using the EVDO network of the same telecom giant that was in the profit sharing agreement with us, and using the same Asterisk server call the IVR for each card activating it.
The obvious advantage was that the moving car would help us spread the load between the tower cells ensuring that we wouldn't strain our telecom-partner's network, which was our main concern :-)
At this stage the gorgeous women had to be let go, irrespective of our wishes. Oh how I cried but nevertheless I Loved my job :) ! The advantages of working in a 3rd world country ! (I kid Colombia....)