In February 2009, ABI Research found that dual-mode cellular/Wi-Fi handset shipments were set to double between 2008 and 2010. With the latter date fast approaching, ABI analysts have confirmed that a similar pattern will hold true - or even accelerate - for the period 2009-2011. This year is on track to see 144 million handsets shipped, with forecasts for 2011 at just over 300 million.

"Wi-Fi's penetration into handsets has more momentum than the bad economy," says industry analyst Michael Morgan.

"It has become a must-have item much as Bluetooth did earlier. But just having Wi-Fi in the handset isn't enough. You have to have a reason for customers to use it. Until now it has been predominantly for data use, with voice struggling to find its niche."

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However mobile operators' attitudes to Wi-Fi have been changing. At first many feared that Wi-Fi would take traffic off their networks, resulting in lost revenue. Now they're starting to realize that it may instead mean an increase in available network capacity.

How operators view Wi-Fi is largely a function of their particular circumstances, says Morgan in relation to the US market.

"Verizon has not enthusiastically embraced Wi-Fi in its handsets, while AT&T has. AT&T was thrown into the pool by the iPhone. Previously people did access data, but the iPhone led people to use Wi-Fi to a degree never seen before. Traditionally cautious Verizon hasn't been thrown into that situation yet, but they are warming up to Wi-Fi.

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Wi-Fi's benefits depend on a carrier's circumstances too. Consider T-Mobile: a wireless carrier that owns no landline assets. It used Wi-Fi (via ‘Hotspot at Home' access points) to deliver an improved in-home service that it couldn't achieve before. In contrast, AT&T does have landline assets. Here Wi-Fi's benefit is to take a load off AT&T's cellular network.

"The picture may be unique to each carrier," Morgan concludes, "but in the end Wi-Fi can offer most operators those two key benefits: extended reach and/or network load reduction."

See also: Wi-Fi and networking news and Smartphone advice