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The auction is due to take place on October 31.
The four companies presented their expressions of interest on September 18. Financially troubled Nextel and cable operator Cablevisión decided not to participate.
A resolution confirming the four participants was due to be published in the official gazette on Tuesday and the winners of the auction are scheduled to be announced mid-November.
The auction for spectrum is long overdue – the last one was held 15 years ago – and the country's mobile infrastructure is reaching a critical point because of a surge in the use of smartphones and mobile data.
Nextel's parent group NII Holdings has been struggling to compete against mobile operators offering traditional mobile services. The company announced in August it would likely file for bankruptcy proceedings in the US.