diff --git a/voip_utils/call_phone.py b/voip_utils/call_phone.py
index 68b48e4..59f84b3 100644
--- a/voip_utils/call_phone.py
+++ b/voip_utils/call_phone.py
@@ -16,11 +16,11 @@
 load_dotenv()
 
 CALL_SRC_USER = os.getenv("CALL_SRC_USER")
-CALL_SRC_IP = os.getenv("CALL_SRC_IP")
-CALL_SRC_PORT = int(os.getenv("CALL_SRC_PORT"))
+CALL_SRC_IP = os.getenv("CALL_SRC_IP", "127.0.0.1")
+CALL_SRC_PORT = int(os.getenv("CALL_SRC_PORT", 5060))
 CALL_VIA_IP = os.getenv("CALL_VIA_IP")
-CALL_DEST_IP = os.getenv("CALL_DEST_IP")
-CALL_DEST_PORT = int(os.getenv("CALL_DEST_PORT"))
+CALL_DEST_IP = os.getenv("CALL_DEST_IP", "127.0.0.1")
+CALL_DEST_PORT = int(os.getenv("CALL_DEST_PORT", 5060))
 CALL_DEST_USER = os.getenv("CALL_DEST_USER")
 
 
@@ -34,7 +34,7 @@
     "sleep_ratio": 0.99,
 }
 
-CallProtocolFactory = Callable[[CallInfo, RtcpState], asyncio.Protocol]
+CallProtocolFactory = Callable[[CallInfo, RtcpState], asyncio.DatagramProtocol]
 
 
 class VoipCallDatagramProtocol(CallPhoneDatagramProtocol):
@@ -42,7 +42,7 @@ class VoipCallDatagramProtocol(CallPhoneDatagramProtocol):
 
     def __init__(
         self,
-        sdp_info: SdpInfo,
+        sdp_info: SdpInfo | None,
         source_endpoint: SipEndpoint,
         dest_endpoint: SipEndpoint,
         rtp_port: int,
@@ -130,7 +130,8 @@ def __init__(
         self.message_delay = message_delay
         self.loop_delay = loop_delay
         self._audio_task: asyncio.Task | None = None
-        self._audio_bytes: bytes | None = None
+        file_path = Path(__file__).parent / self.file_name
+        self._audio_bytes: bytes = file_path.read_bytes()
         _LOGGER.debug("Created PreRecordMessageProtocol")
 
     def on_chunk(self, audio_bytes: bytes) -> None:
@@ -139,11 +140,6 @@ def on_chunk(self, audio_bytes: bytes) -> None:
         if self.transport is None:
             return
 
-        if self._audio_bytes is None:
-            # 16Khz, 16-bit mono audio message
-            file_path = Path(__file__).parent / self.file_name
-            self._audio_bytes = file_path.read_bytes()
-
         if self._audio_task is None:
             self._audio_task = self.loop.create_task(
                 self._play_message(),
diff --git a/voip_utils/sip.py b/voip_utils/sip.py
index 7ff7290..a64c41e 100644
--- a/voip_utils/sip.py
+++ b/voip_utils/sip.py
@@ -64,8 +64,8 @@ class SipEndpoint:
 
     host: str
     port: int
-    username: str
-    description: str
+    username: str | None
+    description: str | None
 
     @property
     def sip_uri(self) -> str:
@@ -346,7 +346,7 @@ def _parse_sip(
 class CallPhoneDatagramProtocol(asyncio.DatagramProtocol, ABC):
     def __init__(
         self,
-        sdp_info: SdpInfo,
+        sdp_info: SdpInfo | None,
         source: SipEndpoint,
         dest: SipEndpoint,
         rtp_port: int,