NOTE: You must have knowledge of Radio + Mobile Network + Cell Network.
With knowledge of Android Studio, C and Java for the app building.
Or have a team of Android + Mobile Network / Cell Network specialists.
Only app builders are not sufficient enough for this task because you need to test. You need to test the app as explained below.
We are in a need of a SS7 protection app to detect when rogue cell towers are in the near. You can make use of an open source application. We have for you the Git available.
You need to verify if the app works properly. You also need to verify the app on security levels: 1) No backdoors - 2) No trojans - 3) No mining - 4) No RDP - 5) etc.
The app should not go off when switching cell towers as this is normal. It also should not go off when switching between cell towers when roaming. It should only go off when a rogue cell tower tries to connect.
Avoid with the app that a rogue cell tower connects with the phone. Block the connection, send a notification to the OS that this is a rogue cell tower so it does not connect.
Budget $400 - $700. Ready in two weeks.