If you’ve got a smartphone with a melody composer, you can program your own darmowe dzwonki na telefon directly through the app. Check your phone’s manual for details on how to do this, but the process is fairly simple.
You can use any sound or song that you own, as long as it’s in a DRM-free format. You can also use a sample of an audio file, but this is less flexible and you’ll likely need to edit it before you can save it as a ringtone.