Stable SMSC with wavecom modems

Hi All

I've already sent this on the users list but I thought maybe the devel
list was a better place to post this.

Has anybody been using wavecom modems and AT2 as SMSC under high loads
both for sending and receiving?
I'm having trouble making it work correctly.
If I'm only sending a lot of messages it works perfectly but if the
receivers of these messages start replying to the messages they get it
screews up.
Some messages are duplicated and others fail completely and doesn't get
send.

Are there any settings I can change to make this work more stable?
I've tried to change the sendline-sleep setting to something higher but
it doesn't help.

Does anybody have any ideas?

Jacob Vennervald