Both the sender and the receiver must be using Palringo for a voice or picture message to be viewed/played from within the chat window. If the receiver is using any other instant messaging service they will get a private link to see the message on our website.
If Palringo is already being used on both ends you still may not be chatting over our network, for example, if you are both using an additional IM service (Yahoo, MSN, etc.). You can tell what your contacts are connected with by looking at the icon next to their name in the contact list.
You can solve this by adding each other as Palringo contacts.