2 Telephone lines and one phone jack

Question

I live in Japan. This means that I have two phones. One is my vonage phone that goes thru the internet and into a regular phone. The other is a DSN style landline for the military base. I currently just have two regular corded phones hooked up to the individule lines. I want to upgrade to a cordless phone, but I only want to have to buy one for both lines. I thought of getting a two line phone, but it seems that even two line phones only have one entrace jack. How would I hook both phone lines up to the one phone?