Back in May I ran a couple of posts on Dual-SIM phones to see how they work in practice (see here, here and here). The secondary purpose of the exercise was to give the phone afterwards to someone using several phones simultaneously due to frequent traveling to different countries and friends in those countries preferring to call and text local numbers.
So while the phone served the purpose of reducing the number of simultaneous phones to be carried very well it had one major disadvantage: No QUERTY hardware keyboard. I was hoping that the dual-SIM capability in addition to Android and the possibility of Internet access and apps would compensate for the inferior text input capabilities of the on-screen keyboard. But it turned out that it didn't.
Even after two months I still got complaints of how cumbersome it was to use the virtual keyboard and calls were frequently missed due to Android's feature of setting the loudness level of the ring tone in idle mode via the buttons on the side of the phone which were often inadvertently pressed.
Back to two phones (+ a third one) then, the QUERTY hardware keyboard of the old phones have prevailed over dual-SIM. Which shows that there is a market besides the main stream where usability is compromised for a bigger screen and a slimness. Hm, that makes me think of my good old N95 and how fast I was with T9 text input and navigating on web pages on the dial pad. Sigh.
Have you tried the Swiftkey keyboard on Android, with prediction and correction?
Don’t Nokia and Samsung offer qwerty dual sim mobiles now? That would seem to be a solution, even if not a conventional “smartphone” one.
I also miss the hardware keyboard of my Motorola Milestone, but typing on my Sony Xperia P with its 4″ screen is passable, especially since I’ve been using Swype. But on a 3.14″ display like your Galaxy Y Duos 6102 has, I guess any input mode is a pain. Maybe your friend should have a look at its 4″ successor called “Galaxy S Duos” which is around the corner: http://www.engadget.com/2012/07/31/samsung-galaxy-s-duos-details-make-the-rounds/
Unfortunately it once again supports only “Dual Standby”.
By the way I’m relieved to see other people unintentionally proceeding to some sort of phonetic spelling (QUERTZ) which is totally illogical in this case as all the correct letters would have been in a row on your keyboard (except the last one if you use a German keyboard layout). I guess this is a result of very fast typing and some automatism fast typers develop. What also happens to me sometimes is typing a word with a completely different meaning that just starts with the same letters like the meant word or sounds similar. Obviously the human brain starts using some weird patterns that sometimes do not match your thoughts if you type too fast.