Software SIP Dialers, also known as SoftPhones are the software that allows you to negotiate called on Android/IOS/PC. These are typically designed to be not that much different than the dialer you use to make conventional calls. They offer voice, video and SMS (messaging) capabilities to other people on the calling network.
I have found a company that provides custom SoftPhones that are "White Labeled" meaning that they can be modified and customized to reflect your brand and offer only the features you want to offer.
Information on the software I use:
https://www.mizu-voip.com/Software/Softphones.aspx
For a flat rate this company can turn out a customized softphone for your application. I have bought the Android and Symbian versions and they work very good.. On many Android phones you can set this dialer up to be the default dialer if you wanticipate on only making private network calls. I have so many of my personal contacts using my system now that this is what I do! It is so nice to not recieve any other calls for any reason except from those people who are on the network.
