diff --git a/fern/advanced/sip/sip.mdx b/fern/advanced/sip/sip.mdx
index 9ddd8419a..dde2bb9c9 100644
--- a/fern/advanced/sip/sip.mdx
+++ b/fern/advanced/sip/sip.mdx
@@ -8,6 +8,12 @@ slug: advanced/sip
 
 This guide shows you how to set up and test SIP calls to your Vapi assistant using any SIP client or softphone. You'll create an assistant, assign it a SIP phone number, and make a call using a SIP URI. You can also pass template variables via SIP headers.
 
+<Warning>
+  A Vapi SIP phone number supports **inbound calls only** because it has a `sipUri` but no public switched telephone network (PSTN) phone number for outbound calls. Outbound attempts fail with `call.start.error-get-transport` and the message `Vapi Numbers Can't Dial Outbound Yet.`
+
+  To place outbound calls, [import a phone number from a supported provider](/phone-numbers/import-twilio) or [connect your own SIP trunk](/advanced/sip/sip-trunk). Use a SIP trunk for international destinations.
+</Warning>
+
 ## Choose your Vapi region
 
 Use the API base URL, private key, and SIP host from the same Vapi region. Do not create a SIP phone number in one region with a SIP URI from another region.