I was working on mobile data sync from last two years but could not find a reliable solution, but finally I found these interesting solutions in both SQL and NoSQL Space-
One in the SQL space called Zumero and other in the NoSQL space called CouchBase lite.
Zumero provides support for SQL lite at the mobile endpoint and SQL Server / SQL lite at the server endpoint.
CouchBase lite supports a NoSQL document based and key-value based databases at both the ends.
Both seems interesting & I am going to experiment further with both of these..