Why does data call hang up on my RST terminal?

After typing the dial string ATDT the Call LED would blink amber, but after about 5 to 10 seconds, it would extinguish, and HyperTerminal would lock up.

This happens if the ‘Settings - Data/SIM -Timeouts - Data RX’ in the Beam Management System (BMS) software is set to a time interval, which is shorter than the time taken for an Iridium data call to be made. 

The recommended default is 40sec.