Just to be clear, are you talking about using the DIGITS service? If so, we'll need to know if you've been set up with the High Speed Data with Paired DIGITS option. That'll allow you to use the data on a second smartphone device. Please take a look at that link and let us know if that's the service you're looking to use.
Please take a peek at my previous post and let me know if you still need more help. Thanks!