Symphony Communication Services, the bank-backed messaging startup taking on Bloomberg LP in a key part of its business, is in talks to raise at least $100 million from new investors. The company plans to use the money to finance an expansion into health care, government, insurance and accounting, according to CEO and founder David Gurle.

In an interview with The Information at Symphony’s headquarters in Palo Alto, Mr. Gurle said Symphony has reached 230,000 individual users globally and 190 corporate accounts. That compares with Bloomberg’s 325,000, although Bloomberg’s users pay $22,000 a year for a broad range of services including data analytics and trading solutions on bonds, stocks and commodities as well as a news service. Symphony’s basic service costs just $20 per user a month and, unlike Bloomberg, it gives discounts to large accounts. Symphony’s messaging business takes aim at an important feature of Bloomberg’s service—an instant messaging system that traders and hedge fund managers use to communicate with each other.