1. A computer system for enabling use of a single voice recognition engine for both command recognition and user speech enrollment, said computer system comprising: a user interface to receive speech input, the speech input comprising at least a portion of a phrase desired to be added to a voice-enrolled grammar; at least one processor; and a computer-readable medium encoded with at least one computer program for performing enrollment and recognition by applying speech input to a turn-based speech recognition engine in one turn that, when executed by the at least one processor, controls the computer system to: process the speech input during a speech recognition turn beginning at a first layer of an ordered stack of grammars, wherein the stack comprises a higher layer, the higher layer comprising an application grammar, a lower layer, the lower layer comprising the enrollment grammar; and a layer between the higher layer and the lower layer comprising a confusable grammar layer, and each layer in the stack includes an exit criterion; wherein the processing in one turn is progressively performed from the higher layer in the stack toward the lower layer in the stack, until a given layer in the stack is reached at which the exit criterion is met; in response to determining that the exit criterion for the given layer is satisfied, end the speech recognition turn, return a speech recognition result based upon the given layer, and ignore any lower layers of the ordered stack, wherein the processing comprises conditionally adding the at least a portion of the phrase to the voice-enrolled grammar based on the processing completing for the lower layer of the stack without satisfying an exit criterion for any layer of the stack for which processing was performed.