If the firmware load is not found on the Load Server, the phone does not upgrade and is not redirected to the TFTP Server 1 or TFTP Server 2.
"On a factory reset or during a software recovery operation, the phone may fall back to using TFTP Server 1 or TFTP Server 2 to recover the phone load. In these scenarios, the phone will recover the phone load either via the term70.default.loads or term71.default.loads file, or it will attempt to recover the phone load based on its load.hist file.
"If the phone is auto-registering with Cisco Unified CallManager for the first time, the phone will request the phone load via TFTP Server 1 or TFTP Server 2. This will only occur once when the phone is first installed into the system. This can be mitigated by preloading the phones with the correct firmware so that no firmware upgrade is required in combination with the auto-registration, or by auto-registering the phones at the main site prior to deployment at a remote site.