Poorad,
Couple questions:
1) Do you have SPA525G or SPA525G2?
2) Firmware version?
3) Please check Bluetooth firmware version (from SPA525 Info page).
4) Beginning with Firmware version 7.5.1 the zip file on cisco.com contains 2 firmware images one with Bluetooth Firmware and one without. If Bluetooth firmware is updated it is a 1 time process and takes approx 5 mins. (look at Release notes)
5) Last reset your Discovery 975 back to pairing mode to clear out the iphone pairing settings and try again.
Randy