Those are erally nice sopranos!!! I used play a curved true tone sop on occasion. The true tones were made by buescher. The true tones are essentially identical to the Conn's of the same time period because Buescher before starting his own company worked for Conn. Based on the serial number, Id say the horn is from the 20s. If its in good condition it fetches upward of about 1200 on average.
For more info on the true tones, check out this link:
For more on the Bueschers in general, try this one: