Currently I use the fring app to take incoming voip calls (currently the only one that can do it!) on my iPhone. This allows me to make calls from my business number via voip on my iPhone while out of the office, which is great but...
It would be a lot better if there was a app available that allowed me to adjust my voipfone account settings, such as divert & voicemail on and off etc, without the need to navigate the website on the 'small screen'. Also it could use the iOS4 features and (as fring does) allow incoming voip calls to iPhones and smart phones.