PBXES Registration from Portugal

Starting on Saturday 15th Sept 3 of my customers (in Portugal) (different sites, different routers and different ISP's) had problems with registering phones to PBXES.
2 customers were set for Nuremburg and the other to Frankfurt.
The problem appeared to be cured but on Monday afternoon it started again on 2 customer sites. Some phones would register but not all.
I switched one client from Frankfurt to Paris server and, on re-booting each phone, they registered.
The problem happened, yet again, this morning on the (now) Paris client. Changing local SIP & RTP ports gave a successful registration and then switching ports back continued with successful registration. Just rebooting without changing the SIP & RTP ports did not succeed in registering the phones.

Have there been any known issues with PBXES or routing on the Internet in France/Germany or Spain as far as you know? It is difficult to identify where the problem lies and, of course, the ISP's are no help at all once things get a little technical.

This post has been edited 1 time(s), it was last edited by ima on 19.09.2007 at 15:33.