GSM and CDMA are two different technologies that are competing in the US. AT&T and T-Mobile are the major players using GSM, while Sprint and Verizon are the ones using CDMA.

There is a huge difference in how SIM cards work between CDMA and GSM. With GSM, the subscriber data is stored on the SIM card. This means you can pop it into any phone with a SIM card slot and it'll just work without needing to even contact your carrier. With CDMA, subscriber data is stored with the carrier. This means to switch a phone over to a different CDMA carrier you'll need for both carriers to work together in swapping over your data, or to use a different phone with the carrier you need to go through them and have them pre-approve it. The reason CDMA carriers use SIM cards at all is because they were forced to adopt it when 4G became a big thing.. It is not even close to what SIM cards do with typical GSM carriers. What's the problem? Well, the majority of the world uses GSM as a global standard and a lot of phones are not built CDMA compatible because the USA is one of the weird cases where CDMA is popular. It's a lot easier for an OEM to build a GSM-compatible phone and just let the user swap a SIM card in and have it work. This is why you normally don't see OEM's selling two unlocked versions of their phones, CDMA and GSM versions. Because CDMA carriers need to allow and support unlocked phones, while GSM carriers can just hand out a SIM card. Recently there have been unlocked phones released for CDMA thanks to popular demand, but to get an unlocked phone working on a CDMA network you still have to get it activated with the carrier instead of just swapping a SIM card. Besides, most of the world uses GSM anyway.

Image source: PC Mag

If you don't know what net neutrality is, check out my net neutrality post. Verizon has made news this week by announcing that their Go90 video service will not count towards their user's data. This isn't the first time carriers have given certain services a pardon, with T-Mobile boasting free unlimited music streaming to certain services. So what's the problem? It's good for the user, so who cares? Who doesn't want unlimited music streaming or video?

Well, the problem here lies in the very problem with violating net neutrality. It's unfair for other businesses that aren't given this privilege. Imagine that you want to create a new company that streams music to compete with Spotify, but something Spotify has that you won't is that streaming Spotify doesn't affect people's' data. This means you're never going to become as big as Spotify unless you're added to this special "VIP" data list. Not only is this bad for that company, it's bad for the user because it curbs competition. Verizon's choice to have their Go90 app free of data charges is even worse than T-Mobile, because they're the ones directly making a profit and stealing users from the likes of other video streaming platforms. While I don't like T-Mobile's choice to have certain music streaming services not incur data charges, I think it's at least more morally acceptable than what Verizon has just done. At least T-Mobile continues to add various music websites to encourage competition. Verizon, on the other hand, has done this purely for selfish gain.

Sources: TechCrunch, T-Mobile