Você que possui qualquer tipo de licença do Flex Builder 3, pode solicitar um serial para utilizar o Flash Builder Beta 4
Flash Builder 4 beta extension serial numbers are available for all licensed Flex Builder 3 customers. This includes all commercial and education serial numbers. To request a beta extension serial number, you will need to enter your Flex Builder 3 serial number, your name, and a valid email address. A beta extension serial number will then be emailed to you.
The beta extension serial number is only available to customers who currently hold a valid, licensed version of Adobe Flex Builder 3. By submitting this request, you are confirming that the serial number you enter has been obtained by acquiring a valid Flex Builder 3 license from Adobe or from an authorized Adobe partner.
Solicite agora mesmo seu serial em https://freeriatools.adobe.com/flashbuilder4beta/