What type of telephone lines can be used for 2-Line CapTel?

What type of telephone lines can be used for 2-Line CapTel?

LINE 1 (voice line)

CAN BE:

An analog telephone line
DSL with appropriate filter (Digital Subscriber Line)
Digital Cable
VOIP (Voice over Internet Protocol)

LINE 2 (captions line)

MUST BE:

An analog telephone line, or
DSL with appropriate filter (Digital Subscriber Line)