Beats Music, the subscription streaming service started by Jimmy Iovine and Dr. Dre, signed up about 1,000 paying subscribers a day in its first month, people with knowledge of the situation said. The company enrolled about 28,000 customers to the $9.99-a-month music service before free trials with AT&T began contributing subscribers, said the people, who requested anonymity because the information is private. Beats Music provided the figures to investors in February, they said. The AT&T tie-in created a pipeline of 750,000 potential subscribers who signed up for 30-day and 90-day free trials starting Jan. 31, the people said. As those trials end, more than 70 percent are converting to paid subscribers, they said. For Beats Music to eventually become profitable, the company will need at least 5 million paying customers, based on an estimate from Recon Analytics in Boston.