I have made a few of my own text tones and ringtones. Some of the ringtones are merely segments of songs that I have not altered - I just sliced out a pleasing-to-me snippet using a sound editor.

The beeps and blerps as I like to call them on the other hand, those require at least some Artistry to create, even though to some degree it can be very simple and easy, if you have the right tools.

I particularly like to use an ios app called Beatwave to make short snippets of pleasant, harmonious chimes, beeps, and short note sequences. I find these really to be quite cheery, which is helpful for something that can often be annoying when someone is blowing up your phone with notifications. :)