AT&F&D0 should work. And, you might want to also try AT&F alone. ATE
and/or ATE1 have proven to work fine also. Check the ATI4 display to
see the factory defaults. The main ones you may need to change follow;

Q0 - Display result codes 
V1 - Verbal result codes 
X4 - Full set of result codes (might be X7 on the
V.90 Sportster) 
&A3 - Display error control and compression
codes 
&B1 - Fixed serial port speed 
&C1 - Normal CD 
&D0 - Override (ignore) DTR 
&H1 - Enable hardware (CTS) flow control 
&I0 - Disable software (XON/XOFF) flow control 
&K1 - Enable compression (auto-detect) 
&M4 - Enable error control 
&R2 - Send data on RTS 
&S0 - Override DSR (always on) 

Next, if any of those differ from what you get using AT&F, make the
proper change to the init string. A hardware handshaking cable is
required.

A Sportster is a user helpful modem. Type AT$ for help with the main
commands. From there, you can see that AT&$ and ATS$ will get you help
with & commands and S-registers.