Intred IP Phone app for iPhone and iPad
"Intred IP-Phone“ is an Internet Telephony based Soft Phone that enables you to receive and make calls on your smartphone. Connection is made to the dedicated central hosted Switching system from Intred. The App enables VoIP calls over 4G and WiFi networks and supports different types of codecs.
Note: you need to have an account from your VoIP provider in order to use this software. This is a supplier specific application and not a generic VoIP service. More information can be found on Intred website.