doc: Add comments on valid phone number format

diff --git a/doc/voicecallmanager-api.txt b/doc/voicecallmanager-api.txt
index c1087f7..94c17d2 100644 (file)
--- a/doc/voicecallmanager-api.txt
+++ b/doc/voicecallmanager-api.txt
@@ -33,7 +33,21 @@ Methods              dict GetProperties()
                                "disabled" - Shows callerid, CLIR Suppression
                                                is used
 
-                       This is usually implemented using the ATD AT command.
+                       The number must be a string in the following format:
+                               [+][0-9*#]{1,80}
+                       In other words, it must be a non-empty string
+                       optionally prefixed with a '+' followed by 1 to 80
+                       characters.  The character set can contain numbers,
+                       '*' and '#'.  Besides this sanity checking no further
+                       number validation is performed.  It is assumed the
+                       network will perform further validation.  The optional
+                       '+' denotes an international number format.  For
+                       example:
+                               +15551234567 - International format
+                               5551234567 - National / Uknown format
+
+                       This method is usually implemented using the ATD AT
+                       command.
 
                        NOTE: If an active call (single or multiparty) exists,
                        then it is automatically put on hold if the dial