Tried to use this app with my companys SIP provider. I had to set up a custom SIP account as the provider was not in the list. Even those though I have no problem with desktop SIP apps, I had no luck with iSIP. I create the account then received random dial tones when trying to place a call. In addition this app has very little support from the developers and show absolutely no polish. Its ugly as sin, difficult to navigate, provides no user feedback or instructions and, as previously mentioned, DOESNT WORK. Dont waste your time or money.