10% of Departing T-Mobile Customers Defect to AT&T & iPhone. What About the Other 90%?

The Cult of Mac noted that:

T-Mobile: 10% Of Departing Customers Leave For The iPhone

Blogger John Brownlee notes that T-Mobile’s plan to offer cheap ($10 per month) subscription plans for cheap (sub-$100) Android phones reeks of desperation.

However, it may be the case that the two are not necessarily tied as tightly together. What if the cheap plans and phones are in response to the other 90% of departing customers?