Facebook is making it easier for people to access its service from their mobile phones. Deals struck with more than 50 mobile carriers in 45 countries will give free access to many features, without any data charges.

This offering, dubbed 0.facebook.com, will likely help Facebook increase its usage in developing countries. Among the countries where people can access the free mobile service are Brazil and India. In Brazil, where Google’s orkut still dominates, Facebook is used by just 2.3% of the population, or 4.2 million monthly active users, according to InsideFacebook.com’s Facebook Global Monitor. In India, just over 9 million people use Facebook, InsideFacebook.com reported.

By contrast, eMarketer estimates that 92.5% of Brazil’s population, or 186 million people, will be mobile subscribers this year, In India, just over one-half of the population, or 604 million people, will subscribe to mobile service in 2010. In China, there will be more mobile Internet users in China in 2010 than the entire population of the US. My colleague Noah Elkin, in his recent “BRIC Mobile” report, writes that Brazil, Russia, India and China (the BRIC nations) have “a high percentage of price-sensitive prepaid users who spend little on mobile services beyond basic voice and text messaging.”

But 0.facebook.com is not solely aimed at developing nations. The free offering is also available from carriers in Austria, Belgium and Finland, among others. And mobile operators in Australia, New Zealand and France are slated to come on board soon.

Overall, eMarketer estimates that there will be 223.4 million mobile social network users worldwide in 2010, representing 4.6% of mobile subscribers and 34% of mobile Internet users.

Facebook has focused most of its attention on growing its computer-based audience. It has more than 100 million mobile users out of a total user base of 400 million-plus. Some believe Facebook will cross 500 million users by June. But with its new mobile service, it has the potential to make its mobile audience grow quickly, too.

I was genuinely surprised (and pleased) by the level of interest in my blog post last week on mobile stats in the BRIC countries. It is certainly the case that some of the numbers are eye-popping, as they inevitably will be anytime you deal with populations as large as those in China and India. But when I wrote the post, I assumed that would be self-evident.

At the same time, I will admit that putting out such lofty projections brought to mind the “data inflation” of the Internet boom a decade ago, when research firms, investment banks and media outlets effectively collaborated in a game of one-upmanship – the bigger the projection, the more coverage it got. Although this was decidedly not our intent, it is hard to put “billion” after anything without recalling the excesses of the Internet bubble.

Skepticism of market projections – born from the previous cycle of boom and bust – was apparent on a number of blogs that cited my earlier post. At eMarketer, we certainly both welcome and encourage the scrutiny. Still, I would again urge readers and those interested in the BRIC markets to not get overly caught up in the big numbers and focus instead on trends in mobile adoption and usage.

For me, the most relevant bits of information are those that reveal the degree to which mobile devices are vital communications lifelines for emerging market consumers – their “all-access pass,” as I describe them in the full BRIC Mobile report. This is as much the case for the farmer working in a remote rural area who can now get up-to-the-minute commodity prices delivered to a mobile handset as it is for the urban consumer who uses a smartphone to post a social network status update. Two highly different settings, user types and need states, but both cases where mobile helps users achieve their goals.

The bottom line: not all of China’s projected 1.3 billion mobile subscribers in 2014 will be created equal. Rather, as I conclude in the report:

In each of the BRIC countries, the mobile user population is divided along several key lines, notably age, income, location (urban versus rural), ethnicity and language, just to name a few. The same holds true for the BRIC countries as a unit. Each country and each subsegment within the BRICs has a distinct usage profile and brings with it a unique set of opportunities and challenges.

My latest report – on wireless usage and advertising trends in the BRIC countries (Brazil / Russia / India / China) – launches today. Given their large populations, some of the numbers are understandably eye-popping. The full report is available here for Total Access subscribers, but here are a few stats that stand out:

• Over 200 million mobile subscribers in both Brazil and Russia by 2014
• 853 million subscribers in India by 2014
• 1.3 billion (yes billion) subscribers and 957 million mobile Internet users in China by 2014

The China stats highlight a key trend I identify in the report, namely that mobile subscriber growth is slowing, but mobile Internet user growth is speeding up. The days of triple-digit subscriber growth are long past. And as subscriber bases solidify, it is now the mobile Internet user populations that are increasing rapidly, albeit from small bases.

They also reveal the degree to which the adage “Everything is bigger in Texas” applies equally to China. Staggering as it may to conceptualize, there will be more mobile Internet users in China in 2010 than the entire population of the US.

Granted, these mobile Internet users do not currently monetize as well as smaller mobile audiences in, say, the US, so aggregate mobile advertising spending levels in China are still low relative to the size of the mobile Internet user base. Nevertheless, the growth trend is significant, and China’s mobile subscribers and Internet users will generate by far the highest advertising spending among the BRIC nations ($223.2 million in 2010, more than tripling to $699.9 million in 2012).

It’s easy to get caught up in the lure of big numbers and overlook the reality on the ground. The fact is that even as a rising number of consumers are purchasing smartphones, many mobile users across the BRIC footprint will remain on less sophisticated devices and legacy second-generation mobile networks well into the middle of the decade.

For marketers interested in reaching the bulk of BRIC mobile consumers today, this means emphasizing messaging campaigns and reserving flashier mobile sites and applications for the small vanguard of smartphone users. By the same token, marketers should also be prepared for changing behaviors as network speeds increase and mobile consumers graduate to more expensive devices and data services.