My thought, however, is that there's a long tail pricing strategy that's being missed. Your plans right now are $60, $175, and $500/mo, which I feel eliminates a lot of folks in the sub-$60/mo region. I'm not sure what the low number should be, but I'd rhetorically ask if you think six $10/mo customers are worth more than one $60/mo customer -- the answer in my mind is no. Building six relationships means that as those companies or groups grow, they'll grow into your bigger packages. As someone at one of those companies leaves their employment and moves to a new job, they'll insist on implementing your technology. They'll tell their friends and colleagues. If you lose one of those six customers, you still have $50/mo coming in. That becomes even more clear when you start thinking about 50 customers at $10/mo versus one $500/mo customer. (I'm not saying $10 is the right number)
I'd also argue that there's a difference between a trial and a free account. If I'm thinking of using this service for some business use case, I personally am not going to let my mind be creative about really thinking how your service can intertwine with my needs if it's just a trial account. I'm not going to invest my time into something ephemeral. But, if there's a free service that I can actually test with a customer and use for a few weeks without that ephemeral feeling, you're starting that relationship building early. Free accounts will absolutely cause you to lose money, which is why it takes testing and analysis to determine the right balance. But if you're actually charging $60/month to send 650 texts, you're already making a profit of 90% after SMS fees and card processing charges.