Hi,
Here is the string I use for the same modem.  Mine is probably not as good 
but these newer modems are forgiving :)
   AT&FS0=0S1=3S2=3X4&A3&B0&H1&K3&R2L1S27=16H0|
It was origionally made for a sportster 14400 and I don't remember if I 
modified it when I upgraded to the v.34+ couriers.
Chris
--- Maximus/2 3.01
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