The best smartphone for Voip calls with WM6

[tecnoxarxa]

Hi !!

Which is the best smartphone for making calls with VoIP and integrated client of Windows Movile 6 ?
No HTC, no working good for it. I'm tested more models and do not work good.

Thank to all !!

[tecnoxarxa]

I like Toshiba Protege 900 with Sip client integrated and Windows Mobile 6

I need test now..