mi consulta es:
1._ existe otra forma de lograr un SIP redirect en asterisk???
2._ se puede eliminar la direccion IP @xxx.dyndns.org y cambiar por una opcion similar a exten=>1000,1,Dial(SIP/$(EXTEN)) de esta forma se comunica con la direccin IP dinamica del telefono asociado de forma automatica. telefonos con IP DHCP.
Firstly, Transfer in Asterisk is not well supported, and handles failures poorly.
For transfers, you always need to provide a SIP URL and that URL must be valid in the context of the upstream user agent. Whether or not domain names other than that of the upstream agent are accepted is determined by the upstream agent. If the upstream agent were Asterisk, it would normally ignore the domain part, and assume the user part was defined locally, but I think it can be configured to actually honour it.
You may find that how the domain is treated depends on whether you transfer before or after answer, as they use very different mechanisms.