I hope this is the right place for this post. I've just bought a Flexor 151 ATA for nineteen pounds on eBay - before realising that it was a discontinued product and that there was therefore no support available from the manufacturer (or the supplier). It works fine when configured to interact with my VoIP provider (DrayTEL) directly. It works fine on incoming calls when configured for 3CX Phone System. However, with 3CX I receive an outbound dial tone but cannot make outbound calls. I can make 3CXPhone on my PC work perfectly both ways, so I would guess my firewall settings are OK. However, the Flexor 151's diagnostic software reports 'Blocking Firewall' when I enter 18.104.22.168 as the STUN server, and 'DNS Problem' when I enter 'stun.3cx.com' as the STUN server. But disabling both the software firewall (BullGuard) and the router's SPI firewall doesn't solve anything. If I enter anything at all in the Flexor's 'SIP Outbound Proxy' box in its account settings, 3CX immediately unregisters it. Short of investing in an approved ATA (I need 7 of the things!) has anyone any ideas, please? Many thanks in hopeful advance.