T-Mobile US Inc. and Sprint Corp. bonds were the most active among high-yield issuers Monday, after they agreed to merge in an all-stock deal on Sunday, their third attempt to combine. Yield spreads on Sprint's most active bonds, the 8.75% notes that mature in March of 2032, were trading 3 basis points wider at 387 basis points over comparable Treasurys, according to MarketAxess. T-Mobile's most active bonds, the 4.750% notes that mature in February of 2028, tightened by 21 basis points to a yield spread of 201 basis points over Treasurys, according to MarketAxess. The companies have $59.5 billion in debt between them, according to FactSet data. CreditSights analysts said the deal is broadly positive for creditors of both companies, citing the long-term goal of achieving an investment-grade rating across the combined company's capital structure. However, they echoed the sentiment of equity analysts, who agree that the deal comes with huge regulatory risk. "This will get significant attention from us and others over coming weeks and the risk are real," they wrote in commentary. The stocks of both companies fell sharply in early trade. T-Mobile was down 4%, while Sprint was down 13%. The S&P 500 was up 0.3%.