Acrobits SIP VoIP phone for iPhone
Linksys (SIPURA) SPA-2002, SPA-1001, PAP2T
Nokia Internet Tablet ( N810, N900 )
Nokia phones with SIP stack ( E61, E70, E71, N95, ...)
Nokia E52 smartphone
Trixbox, FreePBX, Asterisk now
Tutorial in spanish for native Android sip client