In this implementation, the mobile handset continues to operate as it always has (as a GSM or CDMA based device), but now it can be controlled by a SIP application server which can now provide advanced SIP-based services to it.
As device manufacturers exploited more powerful processors and less costly memory, smartphones became capable of sending and receiving email, browsing the web (albeit at low rates) and allowing a user to watch TV.
[1][2] The mobile operator industry business model conflicts with the expectations of Internet users that access is free and fast without extra charges for visiting specific sites, however far away they may be hosted.
Because of this, most innovations in mobile VoIP will likely come from campus and corporate networks, open source projects like Asterisk, and applications where the benefits are high enough to justify expensive experiments (medical, military, etc.).
When moving between IP-based networks, as is typically the case for outdoor applications, two other protocols are required: For indoor or campus (cordless phone equivalent) use, the IEEE P1905 protocol establishes QoS guarantees for home area networks: Wi-Fi, Bluetooth, 3G, 4G and wired backbones using AC powerline networking/HomePlug/IEEE P1901, Ethernet and Power over Ethernet/IEEE 802.3af/IEEE 802.3at, MoCA and G.hn.
Most VoIP vendors implement proprietary technologies that permit such handoff between equipment of their own manufacture, e.g. the Viera system from Panasonic.
Suggesting a mesh network (e.g. WDS) composed of such cheap devices could similarly support roaming mobile VoIP phones.
At this time, some mobile operators attempted to restrict IP tethering and VoIP use on their networks, often by deliberately introducing high latency into data communications making it useless for voice traffic.
The SIP stack and client have since been introduced in many more E and N-series dual-mode Wi-Fi handsets, most notably the Nokia N95 which has been very popular in Europe.
Minor problems were also reported: "Whenever there is an I/O activities ... i.e. reading the Flash space (mtdblockd process), this will create some hick-ups (or temporarily losing audio signals)."
Several router manufacturers including TRENDnet and Netgear released sub-$300 Power over Ethernet switches aimed at the VoIP market.
This made them entirely suitable for VoIP and other low-power use (Motorola Canopy or security camera or Wi-Fi APs) typical of a SOHO application, or supporting an 8-line PBX, especially in combination with a multi-line handset such as the Panasonic KX-TGP (which does not require a powered port).
Accordingly, by the end of 2011, for under US$3000 it was possible to build an office VoIP system based entirely on cordless technology capable of several hundred metres reach and on Power over Ethernet dedicated wired phones, with up to 8 DID lines and 3 simultaneous conversations per base station, with 24 handsets each capable of communicating on any subset of the 8 lines, plus an unlimited number of softphones running on computers and laptops and smartphones.
IP-only providers such as Voipstream had begun to serve urban areas, and alternative approaches such as OpenBTS (open source GSM) were competing with mobile VoIP.