First, you have to realize, that SOA is not something you can buy, install and use. Your existing Enterprise Architecture is most probably is not SOA-ready. It is true especially in case if your company is using such monsters as SAP R/3.

Second, you must realize that SOA does not provide any advantages unless you are link your architecture to the business processes. This is because before you start implement services you must know what services you need. The answer is in business processes.

Third, do not fall for false promises of vendors. They have no idea what SOA is. After all, it was they who sold you all those non-SOA enterprise software in the first place.