Back in the early 90s, mobile phones consisted of a wired handset in a cradle (usually mounted on the passenger side of the transmission hump) and a separate transceiver unit, typically in the trunk (near the antenna, which would be on the trunk lip or rear glass).
The connector in the SVX was simply to provide power for a transceiver unit. There was no other wiring up to the dash area.
Typically this type of phone was installed by the cellular phone companies or authorized agents (e.g., car stereo shops).
See these threads for pics and more info:
Pre wired fro cellular phone
What's this connector for? (posts 1 and 16)