It seems that voxalot's STUN server is unreachable. That's fine for most SIP UAs which have an option to configure STUN manually. But if you want to rely on DNS - no way
Code:
$ nslookup
> set type=SRV
> _stun._udp.voxalot.com
Server: 192.168.5.1
Address: 192.168.5.1#53
Non-authoritative answer:
_stun._udp.voxalot.com service = 10 100 3478 stun.voxalot.com.
Authoritative answers can be found from:
voxalot.com nameserver = ns2.voxalot.com.
voxalot.com nameserver = ns1.voxalot.com.
stun.voxalot.com internet address = 202.60.88.239
----------------
$ traceroute 202.60.88.239
...
...
22 unknown.Level3.net (64.152.102.62) 234.531 ms 233.737 ms 231.873 ms
23 po4-0.cr1.syd1.asianetcom.net (202.147.50.158) 391.914 ms 391.767 ms 392.205 ms
24 po13-1.gw2.syd1.asianetcom.net (202.147.40.130) 384.094 ms 383.756 ms 387.212 ms
25 Pacific-Internet.gw2.syd1.asianetcom.net (203.192.166.150) 392.236 ms 391.398 ms 521.680 ms
26 pos2-0-0.switch1.bne.pacific.net.au (210.23.140.186) 407.643 ms 409.759 ms 408.485 ms
27 * * *
28 * * *
29 * * *
30 * * *