Analysis made by Flash Networks from its installed customer base of mobile operators (serving 30M smartphone users in North America, during the last week of July) found that "Instagram video viewing exceeded YouTube on the fourth of July, America’s independence day, reaching close to 28% percent of total video hits. .. Surprisingly, in comparison with Instagram’s sharp spike, YouTube video hits slightly decreased that day and Vine’s video hits stayed relatively flat .. Google’s YouTube is still clearly the most popular video service, and continues to maintain its superiority in the total volume of mobile video traffic. However, Facebook’s Instagram has demonstrated that it can generate usage rivaling YouTube by being the application of choice for capturing and sharing holiday celebrations".
See also "Avvasi: 'Instagram videos immediately flooded mobile networks'" - here.