My brother-in-law in Kenya has a dual-sim Samsung, not sure on the model. He lives in Kenya where everyone has two or three different mobiles (one for each telco).

It works well, each sim has a different ringtone, and one is set up as a default for outgoing calls, though if I remember correctly it wasn't that hard to switch which line the outgoing call goes through. I believe it was tri-band, bought in Dubai.

Now if anyone can recommend a tri-sim mobile...