By default, you should hear the standard USA ring tone for SP1, and the standard USA "distinctive ring" double tone for SP2. Are you not hearing that?
You can select which ring tone is used for each SPn and you can even futz with the cadence if you like. You will need to be comfortable changing settings in OBi Expert Mode on the OBiTALK portal. You need to first confirm which ring profile, A or B, is being used for the SPn, then edit that Ring Profile's ring patterns (scroll way down the Ring Profile page to see them).
See my screenshot below, and refer to the OBi Device Administration Guide, starting on Page 169:
http://www.obihai.com/docs/OBiDeviceAdminGuide.pdfNote: in order to change settings on the portal web pages, you need to first un-check the right-hand box, then un-check the left-hand box, to unlock the setting for editing. Click the Submit button at the bottom of the page when you are done editing.