I don't think it is just On-Waves. It is probably any cruise ship provided cell carrier that T-mobile could connected to. There is probably a way for T-mobile to disallow any carrier that would charge you on demand. If you call and find out let us know! I did left my T-mobile on last time when I was on a cruise. But I think that cruise line's cell service only work for AT&T and Verizon, so I didn't get any charges.