Well you can use to test for system clocks. 32kHz for real time clock and more like 26MHz clock for processor (faster in modern phones). Up to 2.6GHz you may be able to test RF section also. For example check before and after antenna switch to see if signal has made it through (RX problems) or check if signal is entering PA (Tx problems). With this you can know if PA is faulty or somewhere before PA.
Really it's not a needed tool as you can diagnose most of these problems really by looking at the phone in your hand.
If ringtones are slow or clock is at the wrong time then 32kHz crystal
If processor fails to start, flash it. You can get error messages to say is it RAM, or you can suspect processor clock (vary rare fault...)
No RX - you can test this with network search and see if list of networks is recieved. If so then RX is ok. Else change antenna switch.
No TX - again use network test in phone menu. If list of networks then you have TX fault. So change PA.
These are the most common faults, if you change the IC and fault persists then maybe your frequency tool will be helpful. In 5 years of GSM service though, I never needed a tool like this.
Br
