This is a 24-week, open, randomized, multi-center ICT-based clinical trial conducted in three different hospitals including Samsung Medical Center, Kangbuk Samsung Hospital, and Samsung Changwon Hospital. There are three follow-up measures; at baseline, post-intervention at Week 12, and Week 24. Subjects diagnosed as T1DM, T2DM, and/or post-transplant DM who initiate or currently use insulin therapy will be given education on insulin injection, dose adjustment, and prevention for hypoglycemia and provided at-home measurement device at Visit 1 for screening. Subjects will receive instructions to check daily glucose levels by home glucose meter, to record insulin regimen and dose, the hypoglycemia diary if blood glucose \<70 mg/dL or a hypoglycemic event occurs in the apps, and to synchronize data for automatically transferring to system. Subjects who synchronized their information more than once during 1 week of run-in period will be selected into clinical trial and randomly assigned to either ICT-based intervention group or conventional intervention group at a ratio of 1:1. After the randomization, at Week 1, diabetes educators provide telephone counselling for re-instructing insulin dose adjustment and for re-confirming their use of at-home measurement device and PHR apps at Visit 2 (televisit). Subjects in ICT-based intervention group will have algorithm-based feedback messages when their glucose levels are out of ranges, in addition to recording, saving and sending their data to the server via the PHR app, and those in conventional intervention group will only record, save and send their data to the server via the PHR app. Investigators examine the saved health information such as levels of blood glucose, insulin dose, details on hypoglycemia recorded in hypoglycemia diary, food diary, and number of steps transferred through PHR apps. At each clinical visit, anthropometric parameters, current medication use including types of insulin, insulin dose, and other glucose-lowering agents, vital signs, body composition, and questionnaire for satisfaction investigation are examined face-to-face, and blood tests are performed. The unscheduled visit to clinic could be applied if a subject has one or more severe hypoglycemia (requiring other help for recovery) during the study period, or hypoglycemia (\<70 mg/dL) twice or more times per week, or fasting blood glucose \>200 mg/dL three or more times in the morning, and wants to see a doctor during Week 1-12. The unscheduled visit to clinic is also allowed to the subjects who have difficulty in insulin dose adjustment despite of two or more unscheduled tele-visit. However, even if this criterion does not apply, patients who initiate insulin or change their regimen (eg, from basal insulin once daily to premixed insulin or multiple dose insulin injections) will be allowed to have additional planned doctor visits prior to Visit 3, which is not included in the unscheduled visit, but will be evaluated as scheduled additional visit. The primary outcome will be the proportion of patients who reach an optimal insulin dose within 12 weeks of enrolling in the study without severe hypoglycemia or unscheduled clinic visits.