SOA is not a technology or an implementation, it is a practice of separating services and making them explicit and autonomous with service contracts etc
It is a pattern that you can use on any platform or technology so whether it be .NET 2 or 3.5 you can implement SOA patterns.
Have a read on what SOA is really about so you can design your systems properly
http://en.wikipedia.org/wiki/Service_Oriented_Architecture