Host Route Question

[MissV84]

Phone --> Blackberry Pearl 8100
Unlocked. T-Mobile to Cincinnati Bell
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I went with T-Mobile a few years ago, since there was an issue with getting Cincinnati Bell. I purchased the same phone I'd wanted to purchase with Cincinnati Bell. I am no longer with T-Mobile (My contract was up in November) and have gone back to Cincinnati Bell - the prepaid branch called I-Wireless.
I tried to register my PIN/IMEI with Cincinnati Bell, and was told to do it through my phone using Routing Host. If I do, will it register me to the T-Mobile network or the I-Wireless Network?

edit: I've just hit Register Host, and I haven't received anything yet.