You get charge by a fixed fee, or a percentage of your spending, whichever is greater
Basic gets only customer support, mostly regarding bills and limit raising, other paid plans get technical support
Shortest response times for plans
Developer < 12 biz hours
Business < 1 hour
Enterprise < 15 mins
Enterprise extras
A Technical Account Manager (TAM) acting as a concierge to your support needs, as well as dedicated support team
Free Infrastructure Event Management (IEM), with which lots of engineers, architects and support personnels prepare and be ready to get you through your big events (e.g. Black Friday)
Free training labs
Business plan can pay for IEMs, Developer plan cannot
Business / Enterprise plan can have 24×7 phone, email or chat support, Developer plan can only have business hour email support
The AWS Blog 