For android phones - root you phone, install some patches. Create unlimited accs with restriction of 3 acc per ip, per day.
For iphone phones - Restore as a brand new user. (Not restore from a saved user.) Backup this new user via itunes before creating IG accs. When you reach the 10 acc limits per phone. Restore to this new user and start your 10 acc creation over again. The same 3 acc per ip, per day applies.