asterisk users - Nov 2008 - Linksys SPA 400, 901 and 921 with asterisk

Hello list,

 Topology diagram first:

[PSTN]-----[SPA 400]--------[NETGEAR SWITCH]-------[ASTERISK BOX]
                                                            |         |
                                                            |
|__[SPA 921]
                                                            |
                                                      [SPA 901]

 The problem is the following: whenever i call an outside (PSTN)
destination from the SPA 901
the first attempt is unsuccessful and the second usually goes through.
This problem is only with
the 901 phones, the 921 one works ok. I don't have any problems on the
inside calls.
 The sip.conf, extensions.conf and a sip debug during a call are on pastebin:

sip debug: http://pastebin.com/d41562c84
sip.conf: http://pastebin.com/d5a1fe24d
extensions.conf: http://pastebin.com/d8caeba0

The only thing i have modified beside the sip.conf and extensions.conf
is in features.conf
changing the blind transfer key from # to ##.

 I can provide the configurations from the spa400 and all the phones if needed.

thank you,
v