Most of these modem init strings seem to work very well. If you have a problem that these modem strings don't fix, we are always finding new ways to solve some of these issues.

If you have a properly installed modem .inf file, you normally don't need any initialization string or extra settings when using DUNS (dial-up-networking) - the .inf file determines the init string which - when everything works right - gives you the best connection possible. But, it doesn't always work that way, and sometimes you can improve your connection by adding extra settings (additional initialization string). Many command formats are specific to different modem chipsets. Below the screenshot showing where you go to add extra settings are some 56k/V.34-related commands for various modem chipsets. These commands can be used to enable or disable 56k (V.90, x2, K56Flex, or no-56k- V.34), error correction and compression protocols (V.42/MNP). 

In some cases (especially if your connection is unstable or nearly useless),

To get to the screen for adding Extra Settings:

START -> Settings -> Control Panel -> Modems -> Properties -> Connection -> Advanced

AT should not be used as part of the string, and normally, you should not use &F or Z as these reset the modem to factory, or other, settings which override the settings sent by DUNS based upon the .inf file.

Acer  AT&F2&C1&D2 

BestData  AT&F&C1&D2S11=60L3  AT&F&C1&D2 

Cardinal (Generic)  AT&F&C1&D2\N5 

Cirrus Logic  AT&F&W&W1 

Compaq Presario K56 VSC 
The only way to get this modem online is to put four commas after the phone number. Yes it sounds strange but it does work. 

Diamond Multimedia/Supra  AT&F2W2 

Gateway Telepath modems AT&F 

Generic 28800 bps  AT&F&C1&D2S7=60 

Hayes ACCURA/Optima AT&F&C1&D2 

Motorola ModemSURFR AT&F&C1&D2\K3  AT&F&C1&D2&K3\V1\N3L1S0=0 

Motorola VoiceSURFR AT&F&C1&D2\K3  AT&F&C1&D2&K3\V1\N3L1S0=0 

Mwave (only for IBM 28,800 models) "H%C/N*TH8  "H%C/NS28=18 

MaxTech  /N6 

Packard Bell Modem AT&F&C1&D2 

US Robotics Modems AT&F1&C1&D2&K0  &F1&C1&D2 

US Robotics Sportster 28.8 V.34 AT&FX4&A1&B1&H1&M4&R2 

Wisecom Modems  &FE1L1V1&C1&D2S0=0S7=90 

Zoom 28.8 V.34(i) & (x) AT&F&C1&D2S95=1 

Zoom 56K Flex ATS202=32 

X2 Modems

• Cardinal Connecta 56K 
• Global Village Teleport 56 
• Practical Periferals 56K Data/fax 
• USRobotics 56K 
  • Init String: AT&F1&K0&I0S32=32S15=128S27=64S32=34 
  • Flash Upgrade: 
  • Driver: 
  • Notes: Yes, there are two S32=xxx in the above init string. I'm just reporting what a couple of people have said worked for them.