It is highly probable that anybody buying a Lumia 900 will get a bad one due to a whole host of problems reported by a large number of users. It suffers from defects such as inability of wi-fi to coexist with LTE, poor battery life, vibration rattle, purple tint display, sticky capacitive buttons, phone hangs after a call, self-reboot, camera unable to focus, pink spot in photos, slow screen response, terrible echos during calls, battery sudden drain with heated phone, dropped calls, etc. Many users exchange their phone 2-3 times and some found satisfaction after the 4th exchange only by exchanging for an Android.

WP7.5 is also an immature OS with lot's of missing features and usability issues. Check out this 101 Reasons Not to Buy a WP7.5 Phone now updated with 14 bonus reasons.