French low-cost telecom operator Iliad has set a mid-October deadline to decide whether to improve its bid for T-Mobile US or walk away as it faces resistance from seller Deutsche Telekom, several people familiar with the situation said. Deutsche Telekom, which owns 66 percent of the fourth-largest U.S. carrier, has doubts that Iliad will be able to improve the U.S. business since the French startup has no track record in the country, a source close to the German company's management said.