I want to have a field with autonumbering in ArcGIS. I have a versioned SDE database (SQL server). Thus, using the identity seed attribute in the SQL server is not an option. Is it really not possible to autonumber your own columns in ArcGIS???
Classic problem :(
I can give you a db-specific solution:
The downside of this approach is that if rows get created in child versions and subsequently not posted, you will have gaps in the numbers. You can listen to post events and reassign ids if this is really an issue though.
Until ESRI has a native sequence type, this is the one of the few options you have.
I don't know if the ArcSDE part can do it (a quick search suggests no), but your SQL Server database should be able to auto-increment/auto-number a column of your choice in the data if you want. You can find more information here on how to do it - http://howtoideas.net/how-to-create-auto-increment-column-in-a-sql-server-table