SIEMENS instructions on how to input ringtone:

The following Siemens models are able to accept a manual ringtone input:
C25, C35i, S25, S35i, M35i.
In order to input a tone, in your Menu, scroll to Ringer Tones and Select, then scroll to "Record Melody" and "Select".

The following phone keys correspond to the following functions :

The Number keys:

1 will insert note C
2 will insert note D
3 will insert note E
4 will insert note F
5 will insert note G
6 will insert note A
7 will insert note B
8 will insert note C in higher octave

The Zero 0 key will enter a pause into the sequence.

Holding down a number key will make the note longer.

The # key will move a note up or down one octave.

The * key moves the note up a semitone ("is").