Try contacting this seller:
http://stores.ebay.de/new-media-nord
Doesn't have any refills LISTED, but I think he has them. Is selling the SIM card, so they should also have refills.
Also:
http://www.ecoworldcom.de/ecoworld/framein...eich=10&id_nr=0
Good luck.
I was TOLD that the UM cards will not work, but have never tried.
Stan
Phones: DASH V3 (3)
Service: US T-MO post paid (2) - US T-MO prepaid (2) - UM+ - TravelSIM DE SIMYO - DE SUNSIM T-Mobile DE
Calling Cards: Onesuite Enjoyprepaid AT&T MCI Mobivox