Best wireless VoIP phone?

I work on a diving vessel (oil related) and I'm looking to purchase a portable phone which can work on a wireless network. If possible I would prefer if the phone was not LAN connected, and that the actual phone could pick up the wireless signal.

The portable phones will be used in a compressed chamber to give the divers communication with the boat's telephone line and also so they can use Skype on our wireless network.

Please advise if you know of such product.