I'm going to use Roamer with International SIM card that allows me to receive calls in 90+ countries for free. There're several mobile providers available on the market and one of them is WorldSIM. It provides a user with UK number that you can use in almost every country in the World. So my idea is to use such a SIM with Roamer. In this case Roamer will forward all calls from my home country number to the UK number and I receive them. Everything looks great but Roamer accepts just local SIM cards. It means that if I use this UK SIM card while traveling in USA, Roamer doesn't accept it. And that screws up the whole idea.
I hope the idea is pretty simple and it's worth to be considered. And it could be easily implemented in the application. All that needs to be done is to accept non-local SIM cards.