well, I'm not really a saving expert but i have been on my first half-year overseas training and have taken advantages of every voip apps that provide free trial calls.

but even they're trials, quality sucks and now I have to find a solution for this. Is there any app you know worth paying and rates are reasonable?

Have you used viber? I use it and call India, Turkey and Australia from the US, no problems. It's free and you can call anyone who has downloaded it on their smart phones.

Or what about just buying a sim in the country you are in? You can usually get much better prices on overseas calls on a local sim.

Why not just use Skype? You can call from your cellphone or your computer and can call to any number, any where. The cost is minimal and the call quality generally very good.

I have very good luck with Skype paid calls... clear as a bell and very cheap

Viber is very clear as is Skype. I use both, calling to the US and for people calling me from all over the globe. Once in awhile skype will drop a call but it is rare. There is really no need to buy an app.