Sometimes I need to talk to someone (using PCs on both sides, no landlines) having a very low bandwidth (56K and less). Can you recommend a VoIP service which could provide a connection stable enough for a comfortable talk? No matter how would our voices sound, they must be just understandable and stable.
Don't recommend Skype, it doesn't work at all, can't even sign-in after I go over my traffic limit. I suspect it is explicitly blocked by my ISP (as otherwise it'd work for text messaging at least), so I'd like to have some not-so-popular alternative which my ISP won't bother to block.
I'd strongly prefer a service which can be used natively on Linux, I'd use a Windows-only service only if it is absolutely unique and otherwise great.