[GadgetKen]

I took a few minutes and put the Koko Mobile card in the second sim slot of my phone instead of the Piranaha sim.

Activation online initially showed an activation error, but the fault apparently fixed itself (got welcome to USA message on the phone a few minutes later, so it obviously was working). Added CHF20 to my account online and made a successful test call on AT&T in 4G mode on my phone. Call quality was very good and it went through as a direct dial call. Background carrier for sim card in USA is apparently JT (Jersey Telecom) in the UK Channel Islands (it comes with one UK number you can choose from a list)...not sure if that changes if one of the other roaming profiles for the sim card is used. Didn't set up data yet for the sim chip yet, and probably will normally keep that off since my mifi devices have cheaper rates. Will also have to set up voicemail, decide if I want a second phone number and add additional credit for my upcoming trip.

Bottom line is I now have a functional international roaming sim in the second slot of my phone (the first slot is a USA only prepaid sim).

Glad I didn't wait for Piranha to ship a new sim card. When and if Piranha ships new cards, I'll keep my replacement card as a spare, and put the other sim card in my father's spare phone he keeps as a backup.