For as long as the idea of the 'mobile internet' has been around, we've thought of it as a cut-down subset of the 'real' Internet. I'd suggest it's time to invert that - to think about mobile as the real internet and the desktop as the limited, cut-down version.
Once, the idea that mobile was a subset of the internet made sense. First, the phones themselves could only do a little bit of the internet. That was obviously true for misfires like WAP, as in the Nokia 7110 from 1999 below, and also for i-mode and feature phones, which in theory could load any page on the internet but in practice were very limited in what would work well or at all.
Apple advertised the first iPhone in 2007 as having 'just, the internet', but with everything designed for a big screen that still wasn't the best experience - you still had to pan and zoom, or use a special 'mobile' version of the site.
Second, and partly as a result of these limitations, our mental model of how and where you used 'mobile' was that it fitted into specific, occasional places and times where you were walking or waiting or needed a single piece of information and didn't have a PC - seeing the weather while waiting for a coffee or checking the news headlines as you sit in a cab (ironically, this is now a key use case for smart watches). That in turn shaped how people thought about their 'mobile' site - that you needed to think of 'mobile use cases' and provide only a little slice of your proposition.
These two factors - the limitation of the devices and the idea of how narrowly they were used - led to a mentality that a senior marketing exec at a big FMCG company captured very well for me recently. His team said 'for our internet strategy we have SEO, and SEM, and mobile, and...". And he stopped them and said 'No, mobile isn't part of the internet. It IS the internet'.
Mobile is not a subset of the internet anymore, that you use only if you're waiting for a coffee or don't have a PC in front of you - it's becoming the main way that people use the internet. It's not mobile that's limited to a certain set of locations and use cases - it's the PC, that can only do the web (and yes, legacy desktop apps, if you care, and consumers don't) and only be used sitting down. It's time to invert that mental model - there is not the 'mobile internet' and the internet. Rather, if anything, it's the internet and the 'desktop internet'
So, mobile today does not mean 'when you're mobile'. It means ubiquity - universal access to the internet for anyone at any time. People use their smartphones all the time, very often when there's a PC in the same building as them or the same room, or on the sofa next to them.
If you then ask people about the devices they value, you get a pretty clear answer. This data from the UK shows that mobile devices have overtaken PCs for young people, and (as importantly) for people with lower incomes regardless of age.
The trend is moving fast.
Moreover, this is not just about people in rich countries. Of 5bn adults on earth today, close to 4bn and growing have a mobile phone today, almost all of whom will convert to smartphones over the next few years. The entry price for Android has already fallen to under $40. There'll be lots of grey areas in this - what people pay for connectivity, and to charge their phone - but mobile is a universal product in a way that the PC never was. Indeed, the lower your income, the more valuable communications becomes.
This is the first time that tech has had a universal product - it sold mainframes to big companies and PCs to small companies and middle-class families, but smartphones get used by pretty much everyone on earth - even refugees crossing the Afghan desert.
Then, one needs to think about how these things are used, because that use is a multiplier. We've all seen the data showing that apps represent the great majority of time spent online on smartphones, but there's a much broader point. It's not that apps substitute for the web that matters, but that smartphones themselves are much richer, more sophisticated and powerful internet platforms than the PC web browser. One can argue a little about processing power (though an iPhone 6 CPU has roughly 625x more transistors than the original Pentium in 1995), but that misses the point: these things do so much more than the plain old web, and that's the multiplier effect. There will be many more devices, yes, but more importantly, they'll be used much more and be able to do much more.
This is why thinking about 'mobile' as another bullet point next to 'SEO' misses the point: mobile becomes the platform, and it's a much richer and more powerful one. What happens when almost everyone on earth has a pocket supercomputer connected to the internet? It's not a subset of the internet - it IS the internet.