I got the same problem as you do. I can resolve it by flashing another version of firmware. You can try different version of firmware of your dongle and it must be able to resolve the "dialing" status problem.
內容如下
Version 1.8
Last updated on
Raspberry Pi firmware update "version 5abd572e2ed1811283443387af09377b95501c50 Dec 19 2014"
Debian Wheezy OS update to "Linux raspberrypi 3.12.35+ #730 PREEMPT Fri Dec 19 18:31:24 GMT 2014 armv6l GNU/Linux"
Webmin update to 1.730
Softether VPN update to (Ver 4.12, Build 9514, beta) 2014/11/17
Remove Yate and Minisipserver
Add Kamailio 4.01 Sip proxy (optional). Use defaut UDP 5060 port; not configure
Asterisk update to latest SVN r403917
1. Add CDR logging to mySQL (cdr_odbc.conf)
2. Add Realtime SIP/IAX users for Asterisk (res_odbc.conf, extconfig.conf, modules.conf)
3. Add cron job to check CMPhone drop registration (/opt/scripts/asterisk.sh)
4. Update chan_dongle to match asterisk update
5. Change default asterisk sip accounts from 1000 and 1001 to 2000 and 2001
6. Use UDP 65060 as sip port. Change to other port in sip.conf