I think many projects like these often have more to do about building street cred in the FOSS community than devs providing free tech services for humanitarian reasons out of the goodness of their own hearts. Or one might say that it looks very good on a CV if you are the founder and builder of a free tech service that might be considered a humanitarian cause. Might get your foot into all kinds of doors, perhaps into the oft-shadowy realm of philanthropy, where grant money is can be a huge motivator. I believe there sometimes may be hidden agendas at play as well, perpetrated by wolves in sheep's clothing. Almost all free infotech services have everything to do with data mining and analytics, and nothing to do with helping people in need.

Worth taking note is that while this article states that the phones are "powered by Linux and open-source software", Philtel's own About page declares "To power the telephone network that drives the payphones, we are making use of commodity hardware (especially used/discarded and low-power-consumption hardware) and open-source software where available." This is clearly a broad statement left open to many different interpretations, yet the press specifically leads readers to believe that the project is built upon all free and open source (auditable) code, which is not true at all.

It's likely the "commodity hardware" Philtel refers to are the boards used to replace the coin mechanisms, which look a lot to me like Chinese knock-off Raspberry Pis, and are likely to run proprietary Chinese firmware. This opens up whole 'nother can of worms, and one might see a very clear and nefarious motivating factor if the firmware behind the boards (running the free and open source software) is actually Chinese spyware (i.e. China's version of the Intel Management Engine). The company that makes these boards is called 'Ningbo Joiwo explosionproof Science & Technology co.,Ltd.', and as far as I can tell, is entirely proprietary and entirely Chinese. According to their website, one of the products they make is the "jail phone", or phones that are used by inmates in prison ("Most popular jail phone in America, Europe, and the Middle East"), and as we all know these are designed very specifically for monitoring communications.

Really, there are so many points of vulnerability - from the firmare and provisioning software that runs all the devices involved, to Philtel's own VPS network, which could contain...anything really - that makes the whole project rife for data mining, and we all know analytics is incredibly profitable.

EDIT: It could also be argued that the project specifically targets those who choose to not carry cell phones due to privacy concerns, and where funding may come for something like that is a bit of a no-brainer. Very clever to recuit hackers, artists and engineers to contribute to the project, too. Seems like a great way to keep costs down could be by tricking others into doing your dirty work for you, and making them think they're doing it for a humanitarian or freedom-loving cause.