[Serusers] DNS SRV records

Hi, I am having trouble with my sip-phone recognising my domain name, and I am wondering if I have set my DNS records correctly. If someone can see something that is missing from my DNS record, I would really appreciate some help. So far, I can register using my IP address, but I can't register using sip.mydomain.com, which is what I would like. Any suggestions? Many thanks, Mike $TTL 14400 @ 86400 IN SOA domain1.com. domain2.com. ( 2006051301 ; serial, todays date+todays 86400 ; refresh, seconds 7200 ; retry, seconds 3600000 ; expire, seconds 86400 ) ; minimum, seconds mydomain.com. 86400 IN NS ns1.mydomain.com. mydomain.com. IN A 1.2.3.4 localhost.mydomain.com. IN A 127.0.0.1 mydomain.com. IN MX 0 mydomain.com. _sip._udp IN SRV 0 0 5060 sip.mydomain.com. mail IN CNAME mydomain.com. www IN CNAME mydomain.com. ftp IN A 1.2.3.4 ns1 IN A 1.2.3.4 sip IN A 1.2.3.4