Moody’s Investors Corp. said Monday it has placed T-Mobile US Inc.’s unsecured ratings on review for a possible downgrade, after the company reached agreement to merge with Sprint Corp. in an all-stock deal. At the same time, the rating agency placed Sprint’s ratings on review for a possible upgrade. “Moody’s believes that the combination of T-Mobile US and Sprint will substantially improve the combined company’s cost structure, enabling it to invest in its network as the company prepares to develop capacity for 5G technology applications,” it said in a statement. But there is risk in the integration process that could negate the potential benefits, it added. “If the integration work results in a deterioration in service quality as T-Mobile migrates Sprint customers to the T-Mobile network, churn would increase and New T-Mobile would suffer damage to its newly defined brand and reputation operating as a combined company,” said Moody’s. “The combined effects of increased churn and lower share of gross adds could pressure New T-Mobile’s revenue and cash flow.” In Sprint’s case, Moody’s expects the carrier to benefit from reduced operating and capital investment costs, lower leverage that will bring it to the low 4 times range, improved liquidity, greater operating scale, and an improved market position. T-Mobile’s most active bonds, the 4.750% notes that mature in February of 2028, were 4 basis points wider at a yield spread of 226 basis points over Treasurys, according to MarketAxess, reversing earlier gains. Sprint’s most active bonds, the 8.750% notes that mature in March of 2032, were 3 basis points tighter at a yield spread of 387 basis points over Treasurys.