remove unused import and fix misleading log

gateway/platforms/sms.py

@@ -33,7 +33,6 @@ from gateway.platforms.base import (
     MessageEvent,
     MessageType,
     SendResult,
-    is_network_accessible,
 )
 from gateway.platforms.helpers import redact_phone, strip_markdown
 
@@ -107,7 +106,7 @@ class SmsAdapter(BasePlatformAdapter):
             )
             return False
 
-        if insecure_no_sig:
+        if insecure_no_sig and not self._webhook_url:
             logger.warning(
                 "[sms] SMS_INSECURE_NO_SIGNATURE=true — Twilio signature validation "
                 "is DISABLED. Any client that can reach port %d can inject messages. "