My experience:
Earlier this year I bought a dual sim Samsung Galaxy Ace Duos for my wife (she has her private Movistar phone and her company's Claro phone), she is more than happy with it. The phone is an outdated model, I bought it just because it was the cheapest option with Android and, like you, I wasn't sure how practical it would be and I wasn't up to expending a lot of money in finding out; so I wouldn't recommend that particular phone, but just because it is an outdated model and there are more modern options inm the market like the Galaxy S Duos or, if your wallet can take it, the last generation Samsung Galaxy S4 Mini Duos (which I’ll buy for my wife in a couple months from now).
As for how practical it would be... well it is very practical, the system is very intuitive and works beautifully. I can 0nly think in two cons... and two more cons for a married monger like me:
1. If you are talking in one line the other line goes dead so, if anyone calls you to the other line (the one you are not talking in) the system doesn't give the "busy" tone but the "off line" tone. (I don't think that is a real problem but... that's me)
2. If your phone gets stolen, something not so improbable to happen in Lima, you lose both phones at the same time.
Also, for married mongers like me...
1. You cannot "turn off" the kine phone when you are at home so there is the risk of receiving an unwanted phone call at the worst moment; also if your wife, your mom, your sister etc. asks "please lend me your phone, I've ran out of minutes"... you can't do it because you have 0nly one contacts list, one sms inbox... you get the picture.
2. You have to be very careful when you call a working girl or write her a SMS text because you can, very easily, forget to choose the alternate SIM and make the call or send the text from your default SIM thus revealing your private number to the girl. Or the opposite, you can easily reveal to your wife, friends or family, the existence of your kine phone.
But for many single (unmarried) monger friends of mine, here at the forum, a dual sim cellphone has proven to be an excellent choice.
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