Can I stick my Softbank phone's simcard into a laptop's 3g modem to use internet on my existant dataplan? Are 3g sim cards locked? Would my provider notice?

I have a Japanese Softbank 816sh cell phone with an ‘unlimited’ data plan. The catch is that i have to use their crappy phone browser that can’t really render any websites correctly. They have a super expensive tethering application, but I’d rather just stick my sim card into a netbook with a 3g slot. Are sim cards locked to work only on a certain brand of hardware? Would softbank notice that i’m using internet on a device besides my phone?