I'm in Kyoto this month (from the U.S.). And I had hoped to be able to report about using a rented SoftBank SIM in the N900.

I had reserved a SIM card with SoftBank to pick up at the airport. But when they saw my N900 they argued hard against my taking the SIM card. Apparently some folks have used SoftBank SIMs in their smart phones and racked up huge data charges without realizing all the data access their phone was doing. Then they complain and ugliness ensues. (The data usage charges are on the high side.)

I should have insisted. (My impression was that they would have allowed me to have the SIM after another passionate warning.) I know my normal data usage is rather low because I have a pay-as-you-go data plan w/ATT in the U.S. and I check my usage charges regularly. But I let them talk me out of it. I ended up with a cell phone instead.

So here's my question as I think about some experimentation in anticipation of my next visit. What harm could I possible do by putting the rented phone's SIM in my N900?

Seems like the worst outcome would be that the cell system recognizes the change and cuts me off even after I put the SIM back in the cell phone. Lesser badness would be that it simply would not work in the N900 (for whatever reason) and I put the SIM back in the cell and all is well.

Is there _a_n_y_ possibility of something horrible happening? (N900 blows up? SoftBank police come knocking?)