Iridium 9555 Firmware

Iridium 9555 current firmware: HT21001
(Enter *#91# on your phone's keypad to find out the phone's firmware version)

Download the firmware update tools and Instructions:

HT21001 Compatibility:

  • Iridium 9555 with f/w HT11001 and later, see notes in Instructions.
  • NOT compatible with the older 9555 model (IRID0015), use HT19002 version instead
  • Upgrade tool was tested on Windows 10

List of changes in HT21001:

  • Added optional audible indication of network connectivity status changes (user-configurable).
  • Deprecated support for the older 9555 model (IRID0015). If an upgrade of the older model is attempted the user will be notified with a message indicating the software upgrade is not compatible with the handset. One should use HT19002 for older 9555 handsets (up to IRID0015).
  • 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.

WARNING, please read!

  • Read the entire document with instructions before attempting an upgrade!
  • Phonebook reset. When upgrading Iridium 9555 handsets from firmware versions earlier than release candidate HT14004 all phonebook entries will be lost. Read all phonebook warnings in the instructions document.
  • Inability to downgrade. It is not possible to downgrade to a firmware version prior to HT15002 once an upgrade to HT15002 or later is performed.
  • All firmware upgrades, tools and instructions have been designed, produced, and provided by Iridium Communications, Inc. By performing a firmware upgrade, you will assume all and any risk. Your equipment may be damaged or bricked and costly repairs may be required. Sattrans USA shall not be responsible for any damage to your equipment and/or costs of repair/replacement as a result of firmware upgrades.

Contact us at if you have any questions.

List of changes in previous versions:


  • Leveraged enhancements offered by the Iridium NEXT constellation to improve network connectivity and improve reception of transceiver ring notifications from the core network.
  • Resolved an issue wherein when the user attempted to enter the SMS menu when the outbox on the SIM was full the handset would reboot.
  • Fixed an issue preventing display of predictive help content.
  • Corrected an issue preventing display of firmware version in French.
  • Updated Iridium branding content in Upgrade Tool.
  • This is the last firmware version for the older 9555 model (IRID0015)


  • Addressed an issue where channel assignments were inadvertently being discarded in some situations thereby improving overall handset performance.
  • Modified battery charging algorithm to ensure compliance with battery specifications.


  • Improved accuracy of reporting when SMS storage on the SIM has reached capacity.
  • Added functionality to allow short codes to be stored in the phonebook, used from the phonebook, and dialed directly.
  • Improved responsiveness to power button press to turn the handset off.
  • Improved reporting of signal strength on the user interface and the AT interface.
  • Fixed an issue where a remote DTMF button press could unmute a local handset.
  • Other minor changes (read the instructions document).


  • Calls to the Australian emergency services number “000” are now are permitted when no SIM card is installed in the handset.
  • Added necessary conversions for display of time on user interface in Iridium network era 2 and other era detection and transition improvements.
  • Corrected an issue that would arise when the handset was transmitting and receiving SMS messages at the same time.
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