Greetings,
For an inhouse application we use Wells Fargo as the merchant bank. We use ICVerify (see CyberCash web site). Interface is simple. Start ICVerify to run in background. In your app, create a file with one or more transactions (CSV file with one record per, fields documented in ICVerify manual). Send the file via modem, then wait for response file containing results. Very easy.
John Hines
NewportWave Tech Support
jhines@newportwave.com