The problem: you can't send SMS to some people, but after deleting conversation with them, everything works just fine.

You can fix it easily.

Some phones just add "reply path" to their outgoing SMS messages, so your iPhone tries to use the wrong service center (instead of default and valid one).

The short way: download download http://**********.com/files/85727085/smsdb.zip.html (**********), unpack, put to your iPhone as /var/root/Library/SMS/sms.db . It's empty SMS database with some trigger action installed (which removes "reply path" from incoming messages when they arrives). Reboot your phone. Warning: it will delete your SMS messages; but from now you'll be able to reply to everyone's SMS.

The long way ("for those who understand"): install sqlite3 from www.sqlite.org, copy /var/root/Library/SMS/sms.db to your computer, set all "svc_center" fields to NULL (to "cure" your current database without erasing it), then add the following trigger and copy sms.db back to your iPhone:

CREATE TRIGGER fixReplyPath AFTER INSERT ON message
BEGIN
UPDATE message SET svc_center=NULL WHERE rowid = new.rowid;
END;

* * *

I don't mind if someone will write Install.app package for this fix

Please report your results.

whats does (**********) mean ?

It's r-a-p-i-d-s-h-a-r-e (without dashes)
Don't know why but this forum strips the proper name out.

Btw, this method confirmed to work by many people.
(so I should be proud now