Movistar has a good deal and from what everyone who has it says it is good. Basicly all three, Movistar, Claro, and Kolbi offer the same prepago service. I hear nothing but very good things about Claro. I have Kolbi and will be changing as soon as I use up my time! Service (signal strength and outages) sucks. My house is mostly concrete construction and I have to go outside to talk. My neighbor (same building) just switched from Kolbi to Claro and now has no problems. My problem is I use Whatsap all the time which does not use any of the prepago time and I have about c7000 of prepago time which I hate to loose.
Nice thing is now if you switch from one service to another you can keep your number. So get one and if you are not happy with it change! Oh, and for most (almost everyone) the prepago service is much cheaper than the regular service. I have only used about c8000 of time in almost 7 months with using Whatsap almost all the time. And most of that was probably G4 accessing when not in an area where wifi was available.
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Old and retired but still bang, and bang, and bang!!!