Analog ground-start lines are supported by the FXS ports of the TA900 series, any generation or model.
Syntax is:
interface fxs 0/1
signal ground-start
Please verify that you have a good ground connection to the grounding stud on the back of the TA900, preferably to the same communications ground being used by the PBX. Tip/ring polarity must be kept consistent as well when using ground-start lines.
