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Quick question, when the tests were done on the laptop were they using wifi or were they connected directly to the lan.
Fring is not a SIP softphone, it is for connecting to services like Skype.I run iSIP on my iPhone like this, just for fun in the office, and I have no problems.
The only issue is that Apple doesn't allow apps to run in the background so it will drain the battery if you use it for extended periods, even at idle. It's pretty neat though, has record a call, transfer, and hold.