Midwest SIP has successfully tested a release of Adore SIP Client.

This iPhone SIP client can be downloaded from the iTunes store now for FREE $$$.

Click Here 

Instructions:

Download app to your iPhone or iPod touch.
Click on Accounts
Click Edit button
Click Add new SIP account
in the field for SIP IP, add: sip.midwestsip.com
Add your Midwest SIP username in the Username field
Add your Midwest SIP password in the Password field
turn the account on and make phone calls

I tested the account over AT&T 3G and it worked great although it says it is not supported.
I also tested the calls over WiFi and it worked great.

Make an iNUM echo test call to: 883510000000091 
Make an iNUM latency test call to: 883510000000093