After referring to the Airbus FCOM I can tell you that if they have the standard antenna arrangement this cannot be the SATCOM antenna (its a lot too large for that, too), that should be forward of the middle next to the GPS receivers - I'm not entirely sure, does Swiss have Airphone service on their aircraft? Provisions for satellite TV? Compare it to the antenna that Frontier has installed on their busses:
http://www.luftfahrt.net/galerie/pho...1_Frontier.jpg
Looks relatively similar, at least in size - Frontier is using it for their DIRECTV service.