Much of our attention earlier this week was focused on Twitter’s smartphone app update, a nice polishing of the company’s already decent iOS and Android applications. But there’s another crucial market that Twitter isn’t ignoring: Feature phone customers. Twitter reminded us as much this week, with a series of small yet significant updates focused squarely on lower-cost devices which, unlike smartphones, the majority of the world still owns and uses daily. Among the announcements: Twitter topped off the finishing touches on optimizing its mobile site — mobile.twitter.com — completing a much-needed overhaul of the site, and making it aesthetically congruent with the native application experience. Gone is the unseemly older interface, now updated to be consistent with Twitter’s smartphone apps and the “new new” look of Twitter as a whole. Twitter also struck a deal with MediaTek, a semiconductor company that specializes in hardware platforms and reference designs for “smart-feature” phones. In the deal, Twitter’s application will be integrated into MediaTek’s mobile platforms, preloading Twitter’s app into the middleware. What does that mean? Well, feature phone manufacturers who go with MediaTek’s platform can easily sell phones with Twitter already installed on the device, while the tighter integration makes the app perform much faster, with minimal internal resource use and hardware requirements. Essentially, it’ll get Twitter on a whole lot more low-cost phones right off of the shelf. And on Thursday, Twitter published an app made specifically for the Nokia Series 40 feature phone, offering a native experience on Nokia’s low-cost, widely adopted device. While most of the Western world is focused on our iPhones and Androids, wide swaths of Southeast Asia, Africa and other parts of the developing world are accessing the Web through the lowest-cost computers there are: Feature phones. If Twitter wants to continue furthering its reach, the company needs to make it easier for everyone to access the service across every platform. Concentrating on the low end of the market is just good business strategy. What’s more, it’s also unifying the user interface experience across all devices, a move in line with recent signals that Twitter will be tightening up its ecosystem to third-party developers who aren’t adding significant value in creating outside Twitter clients. Twitter’s ad business is beginning to take off, so the company must assure advertisers that the user base receiving those ads will experience the same thing across the world, no matter what device they’re using. Until smart devices are truly ubiquitous — which is most likely going to take some time — expect Twitter and other smart, mobile-centric companies, to keep the downmarket in the forefront of their minds.