Now the question is how did Mayfield get the phone?
From one of your links:
"Police traced the phones SIM card to a small mobile- phone shop in the multi-ethic Madrid neighbourhood of Lavapies.
From there, police arrested the shops three owners, all of whom have been formally accused of 190 murders and at least 1,400 attempted murders."
I remember reading about some of the bombers owning a cell-phone shop & this being the source of the phones used. Did they send the phones to Portland to be rigged as triggers? Are there records of international shipments?
Possibly some muslim from Spain carried the phones to Portland in his baggage, Mayfield rigged them, and the guy took them back with him. Seems like a long, hard way to get something done when local "talent" was probably available, but anything is possible.
Remember, the Palestinians are constantly using cell phones as triggers in Israel. Any terrorist cell who can't find someone local to rig a cell phone this way is not looking very hard.
I'm not well versed in this area but I think it's not that complicated...just calling the number of the phone sets off the detnator, huh?