You can add Palringo contacts or contacts from any of the supported IM services.
To add a contact all you need to do is open your contact list, tap the + button in the top right corner, select the service the contact is on (you will need to have an account set up for this service) and then enter their id/username or email address. They will be required to confirm that you can add them to your contact list and may not appear until they have done this.
See the Video Guide for more help.