Free VOIP provider on slow internet connection

Hi,
I have tried many VOIP providers like Gizmo, Pennytel, Freedigits, Sipgate, voxalot, and many other but I m not happy with the quality of sound and reliability of service (worst is Gizmo in my case). I have 512kbps connection and I am looking for service provider that uses codecs requiring less bandwidth. I just want to recieve calls from PSTN numbers giving my IPkall number and forwarding calls to my SIP service.

I have 2nd question if someone can give some time to answer. Is their any client that integrates SIP, Skype, Google talk and Yahoo with voice function ?

Thanks for your time reading my post or for any help .

Regards,

Jim.

Likely there is something wrong with the equipment at your end or with your ISP, any of those providers offer perfectly workable connection quality. Try some packet loss tests and experiment with setting some alternative codecs within your own equipment.

It's now possible to integrate SIP and Skype, see items elsewhere in this forum but Google Talk and Yahoo usually need to be run inside their IM API - or take a look at www.meebo.com if you want to run all your IM clients together

Before going further it might be a good idea to check your internet speed. eg.
http://www.testmyspeed.com/

It is the upload speed that is really important and generally the slowest. A very slow upload speed will downgrade your voip regardless of the voip provider. Of the ones that you mention I use Gizmo and Voxalot and for both the sound quality is very good. Gizmo has lately started a Skype/Sip service.

The common voip codecs are here
http://www.voip-info.org/wiki-Codecs

I have used slow speex and the quality of speech is acceptable but I am sure music would be horrible!