This technology (dual sim cards) is very popular and now Samsung is coming up with the 780 model which is one step better than the D880. It is going to release soon but there are other dual sim cards phone around!
One word of caution - You need to clarify whether the particular phone will enable two sim active sim cards at the same time. Some phones will only allow one active sim card at a time. Well, you can try the CECT N99i for an instance. It allows two active sim cards at the same time. It is quite a good phone because I have used one of them. It is not as expensive as the Samsung D880 Duos (costing £200 from ebay.co.uk) but it is alright.