Over time, this issue was eliminated by switch billing instead of billing at the SMSC and by new features within SMSCs that allowed the blocking of foreign mobile users sending messages through them.[citation needed] SMS is available on a wide range of networks, including 3G networks. However, not all text-messaging systems use SMS; some notable alternate implementations of the concept include J-Phone's SkyMail and NTT Docomo's Short Mail, both in Japan.