[asterisk-users] question about sip account format

[Rilawich Ango]

I have 2 sip accounts with name 1234 and abcd respectively.  Account
abcd can make call to 1234 but not visa versa.  When I change account
abcd to 1abcd, both of them can make call to each others.  In the
case, the format of sip account should be start with number.  I wonder
whether we can use a sip account using only characters.  Anyone can
tell me how?  Is it possible?