Call disconnecting groundwire and softphone
This will happen if none of the codecs you have enabled are supported by your provider. Tap on settings, then SIP Accounts, then your SIP Account. Tap on advanced settings, then either codecs for wifi or codecs for 3G (whichever you're using). Move all the codecs to the enabled section, then save the change. If this fixes the issue, you should contact your provider to see what codecs they support.
keywords: call, connect, hang, up, acrobits, softphone, groundwire