Here is the trick to have free SMS service in BSNL while roaming
Just go to your Message settings and change your message center number to +919417399997
and enjoy free smsing while roaming.
More numbers for Free SMS while Roaming
+919417099997
+9194170999971
+9194173999971
If this numbers are not working try by removing + or +91
Note: These numbers will work only in roaming