I received this email as well. I'm surprised that it was not caught by the Sonic spam filter.
That's often the reaction that people have. But these are really tough to block, because of the way that anti-spam algorithms work.
Basically we use a global network of scores, for words and phrases, for sources and senders, for servers and relays. So mentioning "cialis" might be worth 1.5 point, while coming from a relay that's been reported as a source of spam might be worth 1.0 points. Having an invalid return address might add to the score. And when it adds up to more than a certain level, we think it's spam and segregate it.
But this phishing is narrowly focused, and directed only at Sonic customers. It doesn't look like typical spam - no free cruises or off-shore medication etc. And it doesn't trip scores from other carriers who participate in these global clearinghouses of block-lists and triggers.
So - hard to block. And really frustrating. Sorry.