Audio problems on phones (t23g i t42s)

[bob_1921]

Hi,
I have one interesting situation with a series of t23s and t42s phones. Before I describe the problem brief introduction: I have installed over a hundred phone combination t23g i t42s series, on some maybe ten cases the phones are behaving strangely. During the day on some maybe ten phones, happen that three or four calls have difficulties, the audio does not reach the phone. (pbx configuration is ok, also network configuration is ok), when I go to the location where the phone is and I test everything is fine.

The hardware part of the phone is fine, as well as the configuration of the pbx and voip network, it is interesting that when I replace the phone with a new one, the problem disappears and I put the phone that caused the problem in another location and there is no problems, phone work fine ...
I've researched a bit and seen I don't know if I'm right that yealnik requires that RTP ports be set in the range of 11780 to 11800, and that's the configuration on all phones i have instaled.

What do you think, Is this the reason for the difficulty white audio on some phone, because I put this range of RTP port, same on all phones. Do I need to expand the range of RTP ports on the phone and after how many configured phones should it do (Now the range of RTP ports is set to 11780 11800).
Thanks!