However because free (as gratis) version of SFOS has not the Android support and the mobile networking search is a basic feature for every reliable phone which should be as quick as possible available in emergency cases, I strongly suggest to face this issue at native level.
In particular, there are some open GSM strenght signals database available which are reasonable updated. Usually used for establish a geographic position using the GSM towers triangulation.
Therefore, leveraging the last position saved in the smartphone - but not too old - that database in conjunction with the SIM operator detection can be used to instruct the modem towards the best way to deal with the telecommunication network registration and the best mobile data policy to adopt.
This approach might seem challenging but I think that such a challenge has been faced before and properly addressed in GNU/Linux ecosystem. Probably, the wheel should not reivented again.
The benefits will be greater than solely cutting down the network searching time but also in establishing a reasonable geographic position which will helps the GPS to warm up and fixing the satellites.
Moreover, it will give to the user a quick and decent user experience when they use those Android apps which require a position but not necessarly the exact position and it will fix the problem of automatic time zone in native enviroment.
After all, it is about to create a Google Carriers Services native alternative for GNU/Linux enviroment and such a project could be also offered to others companies for money. Because for sure, it is a general problem in many fields like IoT and Automotive markets.