not foss? you dont want free opensource software?
F-Droid
F-Droid is an installable catalogue of FOSS (Free and Open Source Software) applications for the Android platform. The client makes it easy to browse, install, and keep track of updates on your device.
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I want it but I just found call counter and it don't alert me reaching limit...what I need is an alert that told me I'm finishing sms
Here you go. Its a little outdated though but works. Set a plan (your limit) and then set the alerts for % usage
Remember to turn off battery optimisation and all that
Last time I saw a feature like that it was on a Sony Ericsson T300...
and considering that android claim itself to be open source it's very sad
It is open source via AOSP. Which isn’t really relevant anyway.
You can write your own app to do exactly what you need.
https://stackoverflow.com/questions/10723275/count-sent-sms-messages#10723503