The Copyright Office ruled that ringtones-- including monophonic versions-- are subject to the section 115 statutory license: In re: Mechanical and Digital Phonorecord Digital Delivery Rate Adjustment Proceeding.
The short result:
Labels (RIAA) = :)
Publishers (NMPA) = :(
Billboard: Compulsory Licenses Cover Ringtones: "The Copyright Office has decided that compositions used for ringtones may be subject to a compulsory license. The decision is a victory for record labels that want to offer ringtone operators the master rights and publishing rights as one package."
Patry: Ringtone Ruling "Since the amount paid for ringtones may be substantially less than the free market rate, the cost to consumers may go down as to payments to music publishers decrease. I imagine not just RIAA, but celllphone providers are rejoicing."