MacKenzie and Soukoreff have previously introduced a Fitts' Law?based performance model of expert two?thumb text entry on mini?QWERTY keyboards [4]. In this work we validate the original model and update it to account for observed behavior. We conclude by corroborating our updated version of the model with our empirical data. The result is a validated model of two-thumb text entry that can inform the design of mobile computing devices. Author Keywords Mini?QWERTY, Mobile Text Entry, Fitts' Law ACM Classification Keywords H.5.2: User Interfaces, Input devices and strategies