Hi EB, thank you for taking the time to respond.
As it stands, the current RIL only supports up to Android 5.x which (I don't need to say really) is ancient and full of security flaws, with many app developers refusing to support this version of Android anymore.
My reason for saying 7.x is because Android version 7.1.2 was the last release to support 32-bit ARM (armeabi) ABI's (applications) for backwards compatibility. It also still has a broad compatibility with most apps available in the Google Play Store.
I have tried building the supplied RIL driver for 7.x and found the following;
- Initial cellular network connectivity works - signal is displayed and I can scan for cellular networks
- Basic phone calls work (albeit no sound, I don't think this is a problem with the modem, this is Android's fault)
- Data services do not work (the driver only shows 2G / 3G and Android refuses to connect to the APN* (see below)
- 4G / LTE does not work (despite the driver claiming it supports it)
There are some newer versions of the Quectel Android RIL Driver User Guide online that offer support for Android 7.x onwards.
As I said though, Quectel will not deal with individual users directly, they will only supply the drivers and RIL to their business customers and have recommended I talk to the business ie. Teltonika who can request it :)
I acknowledge that the TRM240 / TRM250 are not Teltonika's latest and greatest products but for those of us still using these modems Teltonika is our last hope to get updated Android drivers.
* It's worth noting that using this modem under Windows I can connect fine, there is not a problem with the modem nor my SIM / cellular service