I went to T-Mobile today. This is what I found out.
The guy that works there is a BB user himself but he suggested that I use tech support for setting up tethered internet. He hasn't tried that himself.
Also, the guy said that the roaming cost for out-of-area laptop internet was HUGE and he didn't recommend using the tethered laptop.
So, I guess I won't bother with it. Back to square one for ways to get internet when I visit MIL. Maybe I'll be lucky and one of her neighbors uses an unsecured wireless router that I can connect to, heh, heh.
While I was at T-Mobile, I asked the guy about 4.5 software for BB. He recommended it. So I might download that. I know there's another thread about the BB 4.5, so I'll check it out.