How do I use this code to modify contact ringtone in android?

Question

I found that with code/function I can change the contacts ringtone, but I couldn't find how to use it. Can someone help me, How do I do it?

context.getContentResolver().update(contactUri, values, where, args);
ContactsContract.Contacts.CUSTOM_RINGTONE

One more question. when I call from one android simulator to another I don't hear the ringing sound, what could be the problem?