We've just come across an internal T-Mobile memo that will certainly give a few customers a moment of pause: come April 5th, it seems the carrier will impose new, restrictive limits that affect data usage when roaming. Hot on the heels of the network's roaming pact with AT&T, the change would restrict subscribers to a fixed allotment of roaming data that's proportionate to their current data plan. While most customers are unlikely to notice the change, it's almost certain that some will be left out in the cold. Once the roaming limit is met, users w