As you stated "I try to use ztdummy...", well You need a timing source for MeetMe. 1.6x has a timing source without the hardware, but MeetMe still uses it. You should by any means install ztdummy or maybe Dahdi. Here is what works for me:
rpm -qa|grep dahdi
dahdi-devel-2.3.0.1-0
dahdi-2.3.0.1-0
kernel-module-dahdi-2.3.0.1-0_2.6.18_164.el5
kernel-module-dahdi-xen-2.3.0.1-0_2.6.18_164.el5
lsmod|grep dahdi
dahdi_dynamic_ethmf 15940 0
dahdi_dynamic_eth 10772 0
dahdi_dynamic 14280 2 dahdi_dynamic_ethmf,dahdi_dynamic_eth
dahdi_transcode 12164 1 wctc4xxp
dahdi_voicebus 45248 2 wctdm24xxp,wcte12xp
dahdi 197320 24 opvxd115,rcbfx,r1t1,rxt1,ax1600p,dahdi_dynamic,ap400,ystdm16xx,ystdm8xx,opvxa1200,xpp,dahdi_transcode,wcb4xxp,wctdm,wcfxo,wctdm24xxp,wcte11xp,wct1xxp,wcte12xp,dahdi_voicebus,wct4xxp,wanpipe
crc_ccitt 6337 2 wctdm24xxp,dahdi
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