Frankly, I wonder what the motives really are for most people. It seems that everyone has gone mental about reducing their phone bills. I see people with a very comfortable salary who will go out of their way, spend time and effort, risk losing their number and the capacity to phone for weeks, tie themselves to long (typically 2 years) unchangeable contracts for saving, maybe, 5 or 10 Euros a month. Sorry, but I don't get it.
It is a behaviour which defies logic. Besides, most people save pennies on their calls, but are fools for anything else. They spend 2-3€ per ringtone which they change every week while it is quite easy to use any free mp3 as ringtone. They fall for 2 years contracts because they want to buy the "latest" phone for free. They use premium sms at 2€ for 140 bytes. They send mms pictures when in vacation at 5€ the mms, etc...
I don't get it. I could, with a stretch of my imagination, understand why it is important, for many people, to be seen with the latest iPhone whatever the price is (for example). I don't get it when, at the same time, their motivation to have it jailbreaked is to use voip. That, and fake Rolex or Vuitton bags, I don't get. Sorry.
Besides, telcos have an ace up their sleeve: they can always lower call rates to voip levels. I explained why this technically a better solution for them. I can also say that they can afford it: call charges make only a fraction of their business nowaday (less than half in Germany). Of course this may not be sufficient, since the customers are not rational in their choice and strongly believe that voip is "free" while cell rates are "expensive" whatever the price actually is.