Why do so many people seem to have to phone someone just to shout "Hi. I'm on the train...yes the trainI know your being funny, but that scenario is not unusual at all here in the Philippines. Here in this part of the world, all major carriers offer unlimited text and call plans to its consumers. One carrier even offers P10/30min ($0.25/30min) plan for 3G/GPRS service.
....now Its leaving the station.... bye".
And then on the intercity trips there is always someone next to you that obviously uses his phone for business but has that really loud ringtone of Abba singing "Waterloo". He always puts his phone back in his pocket after each call and then takes 20 seconds to get it out again when he's called two minutes later.
Trains are uncommon, so you'll hear this instead: "Hi. I'm on the jeep...yes the jeep.... I'm stuck in the traffic....bye".
I guess it all depends on the market. If a carrier won't offer an unlimited plan, its competitors would quickly eat up their market share. The consumers, which are mostly composed of teenagers, are notorious for buying multiple SIM cards from each carrier to take advantage of whatever unlimited plans are being offered. Network lock-ins are unheard of. Sell a network-locked phones to Filipinos and either one of these will happen: (a) It won't sell. (b) It will be circumvented.