Here you can find a detailed manual how you can activate the SMTP authentification on an iPhone.
Open the Settings. Click on “Mail, Contacts, Calendars”.
Select the account to be modified here.
Click on “Account Info”.
Click on SMTP in “Outgoing Server”.
Select “smtp.nine.ch” in “Primary Server”.
Enter the same access data here as for the incoming server. Your user name corresponds to the email address. The hostname is smtp.nine.ch.