If you open Hoiio iPhone app, you can see the similarities between Hoiio and iPhone native Call/SMS applications. 

Hoiio has four main menu that is displayed at the bottom of the application. You can call your friends or send SMS to your loved ones by accessing Call and SMS menu.

For other advanced features like roaming, exporting your mobile contacts to Hoiio, topping up/recharging Hoiio credit or inviting your friends, you can tap More.

To change login details, country code, Call From number and caller ID, go to Settings.