A large-scale attendance, productivity, activity and availability biometric control method using the telephone network, for individual client users with speaker verification technology based on limited enrolling data and short verification sentences. The method includes the steps of registering and enrolling a client user; generating, storing and indexing a template and a reference average spectrum with a client user PIN; prompting the client user during a future verification event to pronounce the enrolling/verification sentence associated with the PIN to provide a speech signal; estimating a verification distance between the PIN indexed template and the speech signal pronounced by the client user, using the PIN reference average spectrum indexed; validating the telephone number; deciding if the pronounced speech signal pronounced by the client user has been validated based on the verification distance, with unsupervised compensation of the noisy input signal's spectrum if its difference from the speaker model is small, instead of adapting the user model spectrum; optionally repeating the steps of prompting, estimating, validating and deciding for a limited number of times; and accepting or rejecting the future verification event.