Dish Network, Sprint’s other suitor, has declined to raise its offer after Sprint won support from a major shareholder following Softbank's decision to up its original bid.
Son was speaking at an annual shareholders meeting, and a final decision is expected next week when the company is due to vote on Softbank’s offer.
Sprint also took an advantage over Dish in its battle to secure control of Clearwire, after raising its buyout bid to $5 per share, as both companies seek wireless airwaves on the networks to increase capacity.