Here are my steps and results. I have an Iphone 3G with AT&T. I am on the "Data Plan for iPhone" data package, and also have the "iPhone Text Messaging Unlimited" plan for SMS. I have an individual account with a 17% corporate discount through my employer.
Steps:
1. Downloaded SwirlyMMS 1.2.8 from Cydia
2. Paid $8 for the full license (support you guys no matter what!)
3. Downloaded the Blackjack 2 settings and installed per instructions.
4. Sent test mms and instantly got the following error: "Failure - You don't have an active GPRS/EDGE/3G connection for the moment! This can be due to a temporary problem in the Network or that your APN setting are incorrect. Please verify your APN settings on the setting page." FYI the message did not go to the outbox.
5. Rebooted iPhone
6. Launched Swirly, created and sent a new mms. I got the "Sending..." message for 3 minutes, then an error: "Failed to send MMS - Possible incorrect MMSC setting. Unexpected HTTP response (HTTP/1.1 403 Forbidden)" This time the message is in the outbox.