I'm finding myself using a lot my sipphone accout, but here the dilemma ...
I tried first the rtcomm osso account plugin for sip, it works ok, sometimes, the sound quality iisn't the best, but the major turn off it's when I answer a call.and I don't hear nothing, but when I do an outgoing call works.
Then I tried the gizmo5, which works ok, but sound quality it's a little better, but if you open the browser and other things it's too much.
Now, I tried Fring, which surprised me, as it's a hog using memory, more lightweight than gizmo5.
But sound quality, it was better!! Doesn't sputters or lag, connections are faster, very nice...still lacks of an icon tray option..
I have not tried Fring, but I found the best quality to be the rtcom client. And yes there is that issue of not hearing the other person sometimes, but there is a lot of threads that have talked about this. I found that if I leave the internet call application open and just minimized (as you would with fring, or gizmo) it works perfectly every time. Another guy say when he can't hear the other person he messes with the volume and suddenly he can hear them. It is a weird qwirk with the application. But the lightweightness and auto log in when I roam to other wifi hotspots is so perfect. The sound quality is excellent for me. Maybe you should check(play with) your advanced settings. Also it could be your internet connection.
Again I have not tried Fring but I am a huge advocate for rtcom having been a huge skype and gizmo user.
My experience with the clients and Gizmo / Google Voice.
Rtcomm / osso sip / internet call :
everytime I answer incoming, it disconnects.
everytime I make outgoing, it's hit or miss as to whether or not myself and the other party will be able to hear each other. (even when i leave inet call open).
Is there something I'm missing, I've heard leaving it open fixes problems, but for me its ~80% fail rate.
it would be preferable to use, however, considering I use it for my IM'ing.
Gizmo client:
Works very well. Never a problem. However, as stated, very heavy.
Fring
Never tried it, but planning on it.
///EDIT
Just installed Fring. I like it, except for the lack of DTMF dialing. Otherwise, it seems to be reliable.