I found the following information about character conversion tables..

This configuration file describes the SMS Center default character set.

s2aupsamplemx.cf (the user profile file)
The applied character conversion tables can be defined in each application's user profile. for example:
character table file = /etc/opt/nokia/smsc/conf/xtm_isolat_mx.cf
special character table file= /etc/opt/nokia/smsc/conf/xtm_special_mx.cf

But if the default alphabet extension table (the table which includes characters [, {, ~ and so on) is in use..
Where the extension table is defined? In the xsm_smchar_mx.cf file or in the user profile file? Or can it be defined only in user profile file?
And how it is defined? Something like
extension character table file=/etc/opt/nokia/smsc/conf/xtm_extension_mx.cf