te120p and music on hold

We are using asterisk 1.2.24 on linux 2.6.18 . Our users tell they ramdomly are put on hold, earing mosiconhold, both legs of the call. So, when this happens, neither can resume from musiconhold and the only thing to do is to end the call.
Also, time to time calls are ended ramdomly, without any reason, at first
glance.

Zaptel.conf is

loadzone=it
deafultzone=it

span=1,1,0,ccs,hdb3
bchan=1-15,17-31

they have only ten lines on pri

Zapata.conf is

[trunkgroups]

[channels]
language=it
immediate=no
echocancel=yes
echocancelwhenbridged=yes
echotraining=yes
callerid=asreceived
switchtype=euroisdn

context=from-mypstn-custom
;context=from-zapata
signalling=pri_cpe

overlapdial=yes
;pridialplan=national
pridialplan=unknown
prilocaldialplan=unknown

internationalprefix=00
nationalprefix=0
localprefix=02
privateprefix=******* ; for privacy j naked this value.
;If You need it j can unake

priindication=inband

;immediate=no

usecallerid=yes
hidecallerid=yes
;usecallingpres=yes

group=1
channel=>1-15,17-31

Does someone have any suggestion?