Even with the more relaxed approach to large mergers, which many expect from the current US administration, the much-rumored plan for Sprint and T-Mobile USA to join forces would still be a tough one to get past antitrust regulators without major concessions. Masayoshi Son, chairman of Sprint’s parent Softbank, is said to be exploring other options, including short term investments from Liberty Global or even super-investor Warren Buffett, according to The Wall Street Journal. The Journal reported that Son had met separately with both Buffett and with Liberty’s billionaire chairman John Malone, at an annual gathering of CEOs in Sun Valley, Idaho. One option, unnamed sources said, would be to have Buffett’s Berkshire Investments injecting over $10bn in cash into…