Is anyone using a replacement SMS app for Treo 650? (Mine is Verizon.)

I've seen requests for info on this in other threads, but no answers.

What I particularly want is an option for a subject line.

When sending SMS to a phone this might simply appear in parentheses, as happens now when someone emails to my SMS address -- i.e. the recipient would see:
"(hi) what's happening?"

When sending the same SMS to an email address, the recipient would see:
To: recipient
Subject: hi
what's happening?

This matters to me because I can send instant messages to my company's internal system if I can send a subject line.

Palm's MMS app allows subject lines, but it pretty much never works for me --as others discuss in other threads, messages sent and received are delayed for hours or days or simply never arrive. I'm looking for another substitute.