SoftBank is the Japanese telecom that last fall agreed to purchase a 70% slice of Sprint for $20 billion. The DISH counteroffer is for $25.5 billion. Sprint announced last week that it had formed a "special committee" to review DISH's unsolicited offer.
Sprint received the waiver from SoftBank on the condition that the company not disclose any non-public information to DISH during their talks and not enter into negotiations with the satellite pay-TV provider.
The U.S. carrier said it does not intend to make any further statements about the DISH proposal until it assesses whether that offer is or could be superior to SoftBank's merger agreement.