A new study by User Centric, a Chicago-based usability consulting firm, claims that iPhone users make more typos than those using phones with full keyboards or phones with numeric keypads. Despite the extremely small sample size of only 20 users to a group, the researchers found that iPhone users entered text as quickly as their counterparts, but made significantly more errors — 5.6 per message, compared to 2.1 and 2.4 for full keyboard and…