Not an app, but https://quackr.io/ Its also not the only one, but thats the one I remember More on reddit.com

I went down this rabbit hole a while back when I needed to test onboarding flows too, and most of the sites offering disposable numbers either did not work or felt shady enough that I did not want them anywhere near my info. What ended up working for me was using a tool that gives you real, functioning numbers you can recycle or delete whenever you are done with a test. I use Cloaked for this since you can spin up as many phone aliases as you want and they behave like actual numbers, so verification texts and calls come through without any hassle. When you are done you just turn that number off and your real one stays completely separate. It also manages everything in one place so you do not end up juggling random services. Before that I tried a few of the SMS receiving sites and half the numbers were already burned or blacklisted. Having something stable that does not expose your real number to whatever platform you are testing is way less stressful. Hope this helps! More on reddit.com

I don’t understand why you’d want to go through all this headache when services like 100⁤1SM⁤S and similar ones exist. For just a few bucks, you can save a huge amount of time. More on reddit.com

SL is planning to add phone numbers, to what extent I do not know. However my personal estimation would be that it is a fixed number, to hide your real number (=you don‘t have to give our your real number), sort of in a way of what Phoner does. This due to regulatory issues. However I am very curious with what they will come up with. More on reddit.com