Japanese carrier NTT DoCoMo will launch flat rate data billing for smartphones, tablets and data only devices, starting March 15. The plan will give customers a choice between two-tiered or full flat rate billing to suit their data usage habits. The two-tiered option lets users pay as they go for moderate data usage up to a set limit, or pay a flat-rate monthly charge of JPY5,985 ($72.5) if they exceed the set limit. Under the full flat-rate option, the monthly charge is JPY5,460 ($66.1) regardless of data volume.