Iridium has released firmware update HT21001 for the Iridium 9555A model of satellite phone. Important note: This update only applies to the 9555A model, previous versions of the 9555 are not eligible for this update. Customers with older 9555 models should update to version HT19002 using this link.

• Added optional audible indication of network connectivity status changes. User-configured in Menu > Setup > Volume and Tones > Network Tone.
• Deprecated support for 9555 model number IRID0015 (9555 non-A). If an upgrade of this model is attempted the user will be notified with a message indicating the software upgrade is not compatible with the handset.
• Improved communication channel selection algorithm used when establishing a connection with the network in telephony mode.
• Added stronger validation checking of periodic radio calibration changes before storing to persistent memory in telephony mode.

The firmware update file along with the instructions can be found here.

Note: The firmware update utility is not compatible with Mac OSX.