Take a look at this video on receiving PSK-31 with your iPad / iPhone. http://youtu.be/CJslXYD6-4Q (http://youtu.be/CJslXYD6-4Q) The app is only $2.99.
Doing this through the iPad / iPhone may not be really practical in a true SHTF or WROL situation; but it might serve as another option for doing digital modes if your laptop goes tits-up!
K7AGE makes reference to an interface that you can get off evilBay. http://www.ebay.com/itm/EASY-DIGI-PSK-INTERFACE-FOR-IPhone-IPad-IPod-Touch-/221170345121?pt=LH_DefaultDomain_0&hash=item337ec7a4a1 (http://www.ebay.com/itm/EASY-DIGI-PSK-INTERFACE-FOR-IPhone-IPad-IPod-Touch-/221170345121?pt=LH_DefaultDomain_0&hash=item337ec7a4a1)
I just bought one a few minutes ago.
A review to follow...in the meantime I'm going to test the app and technique this weekend just to see how well it works.