1. A method for performing speech recognition, comprising: storing, by a processor, a plurality of rules associated with performing speech recognition, at least some of the plurality of rules being based on constraints associated with a subject matter of a voice input; receiving, by the processor, a telephone call from a caller; determining, by the processor, a telephone number from which the telephone call was made; retrieving, by the processor and from a first database, information associated with the telephone number; receiving, by the processor, a first voice input from the caller, the first voice input including information regarding a model year of a vehicle; generating, by the processor, a first speech recognition result corresponding to the first voice input; identifying, by the processor, a first group of the plurality of rules based on the first speech recognition result; receiving, by the processor, a second voice input from the caller, the second voice input including a plurality of characters in a sequence, the plurality of characters corresponding to a first vehicle identification number; generating, by the processor, a second speech recognition result based on the second voice input using the first group of rules, at least a first one of the first group of rules being associated with identifying one or more of the characters in the sequence and being constrained to identify one of a subset of possible characters based on a position in the sequence; comparing, by the processor, the second speech recognition result to the retrieved information; increasing, by the processor, a confidence value associated with the second speech recognition result when the second speech recognition result matches at least a portion of the retrieved information; calculating, by the processor, a value using the second speech recognition result; comparing, by the processor, the calculated value to a portion of the second speech recognition result; increasing, by the processor, the confidence value associated with the second speech recognition result when the calculated value matches the portion of the second speech recognition result; providing, by the processor, a first prompt to confirm a second vehicle identification number based on the second speech recognition result being associated with the increased confidence value; receiving, by the processor, information indicating that the second vehicle identification number does not correspond to the first vehicle identification number; applying, by the processor and based on receiving the information indicating that the second vehicle identification number does not correspond to the first vehicle identification number, a second group of the plurality of rules to the second voice input, the second group of the plurality of rules being different than the first group of the plurality of rules; generating, by the processor, a third speech recognition result based on applying the second group of the plurality of rules to the second voice input, the third speech recognition result corresponding to a third vehicle identification number; and providing, by the processor, a second prompt to confirm the third speech recognition result.