I'm now using "paranoidandroid" (acka old D4) ROM.
Has native voip installed and does work !
I've done side by side comparisons with Csipsimple and the latter is by far better call quality including reception, echo, volume and clarity.... even on the standard csip settings.
I've gone looking for how to change codecs with the native installer but no luck... then again, csip simple still better with the standard codecs , even discounting G729 etc.
be pleased if anyone can get native working well as the csipsimple is STILL NOT AS GOOD AS MY OLD Nokia. humph !