[Zenst]

Often the case and one excuse they provide is so that they can comply with radio regulations - which as many are semi software with DSP's in effect, would make the slightest software bug/change cause issues with the local radio regulators and indeed, the telco's. Not saying that you would need a radio licence from the local area just to compile modem code, but maybe not that far removed in part. Certainly testing, would dictate a sheilded enviroment to avoid legal issues and then at the end of all that, it would have to be certified by whatever local regulator of the country(s) it is used.

So does make open source modems rare, liability exposure of legal fallouts make for some muddy waters.

[zzo38computer]

It would still be possible to be open source, even if it cannot be altered, such as by storing it in ROM (or storing a checksum so that only the exact version will run; this works better if the program is written in assembly language, since then you do not have to worry about the compiler messing up stuff). It could also be designed allow the code to be uploaded but to disallow transmission in that case, making it so that if the code is altered then it can only receive, and cannot transmit. Another alternative might be that the radio and the DSP are separate components in a single package, and then if you want to use them separately you will have to break the package to reveal the parts, and then it cannot be resealed; you will have to make your own and lose the warranty. (This last alternative is what I think is good, but if that won't work (I don't know much about its working, so maybe it won't work) then the others ways might do.)

[wbl]

For the cellphone service. In ham land you can do anything that follows the emissions rules.

[FlyMoreRockets]

> In ham land you can do anything that follows the emissions rules.

In the US, hams are prohibited from employing encryption with the single exception for control coms with amateur space-based radios. With the proliferation of digital modes, the encryption rule is increasingly being challenged and it will be interesting to see where this goes in the future.

[otterley]

In ham land, the transmitter possesses the license to utilize the radio spectrum. With mobile phones, the carriers do. Cell phone owners don’t need a license - the model assumes their equipment manufacturers do, and will do what’s needed to assure continued compliance.