• by Laurie Sullivan , Staff Writer @lauriesullivan, June 11, 2014

Google, Facebook, Yahoo, Microsoft, and other companies all have a mobile-first strategy, but determining the regions where brand marketers should initially invest in mobile campaigns may seem a bit more complicated. Any brand marketer or supporting agency partner that is surprised by the eMarketer estimates that 1.76 billion people will own and use smartphones monthly this year -- up more than 25% compared with 2013 -- needs to reboot. By 2017, the number will rise to more than one-third of people worldwide. Here are some factual estimates that might help ease the confusion.

The United States remains the second-largest smartphone market worldwide, behind China, totaling 163.9 million users in 2014, eMarketer estimates.

Consumers in Asia-Pacific will account for more than half of all smartphone users this year, totaling 951 million. South Korea leads in terms of penetration, followed by Australia. This year, smartphones in Japan will reach half of all residents. China will not take the status of supporting the majority of its residents until 2018. Smartphone use today in the country totals 521.7 million.

With 196.6 million, eMarketer estimates that Western Europe this year will become the second-largest region in terms of the number of smartphone users. Three Nordic countries reached 50% penetration last year, and this year the Netherlands and United Kingdom will join them. In 2015, the remainder of the EU countries will make the leap to majority status, per eMarketer.

By 2018, Forrester Research estimates that Asia, Asia-Pacific and Oceania with have nearly 2.4 billion unique mobile subscribers -- up from nearly 2.2 billion in 2013. The Middle East and Africa will see subscriber rates rise from nearly 792 million in 2013 to 981 million in 2018, and Latin America and the Caribbean from 370 million to 415 million, respectively.

When it comes to mobile subscribers by region, Latin America and the Caribbean will grow from 693.7 million in 2013 to 765.7 million in 2018. Asia, Asia-Pacific and Oceania will see the growth rate rise from 3.5 billion to 3.8 billion, and the Middle East and Africa from 1 billion to nearly 1.3 billion, respectively, per Forrester.

Among the many reasons for the increase, accessing email on mobile devices continues to push up smartphone adoption. Email open rates on smartphones or tablets climbed to 48% in 2013, up 33% from the prior year, per IgnitionOne's Knotice email marketing division, which the digital agency acquired in March. The highest open rates for the day on a smartphone are between 5 a.m. and 7 a.m., and then again between 7 p.m. and 10 p.m.

Not surprisingly, Apple's iPhone takes the top spot for email opens and readings at 82.51%, followed by the Samsung Galaxy S III SCH I535 at 1.16%.

While mobile ads accounted for a little more than 1% of all impressions, the ads drove 2.5% of actions, per Neustar Localeze. The report Cross Device Local Search suggests that mobile phones have the highest conversion rate, with four out of five local searches ending in a purchase, though three in four of those purchases take place in a bricks-and-mortar store.

"Man looking at smartphone" photo from Shutterstock.