A wide variety of customer equipment is used on the VoIP User network including desktop VoIP phones, softphones, mobile phones (using Fring on the Apple iPhone and Windows Mobile devices and in-built Wi-Fi functionality in Nokia E series), ATAs and open source switches and PBXes like FreeSWITCH and Asterisk. As VoIP User is a "Bring Your Own Device Network" best of breed solutions can be used by the end user. VoIP User enables these devices to be mapped to UK non-geographic numbers (typically 0844 or 0870) that have a per minute call rate low enough to fit in with VoIP User’s mode of operation. As an experimental network, several software vendors and private authors test their SIP devices using the VoIP User network. As of January 2009 there were over 250 SIP User-Agents known to VoIP User.