My VOIP is mynetfone. I have used it since 2006. It is a good service. I have a supersave account, pay as you go, no monthly fee. Price is very fair. Local and std calls cost 10 cents. It has web SMS service, global access call-back, global access call-in. but things needed are: a local call numbers in some regions (ie Armidale), web call connection interface etc. Both Ekiga and Twinkle at linux handle this voip well.
Recently, tried android apps of mynetfone. Both voip and SMS on MNF work well.
I’ve been using mynetfone for a while. Highly recommend.
as I said, I am a happy user, but want a bit more functionalities.