I KNEW this someone was going to ask me this. Of course it would be you [USER=640]@JQuinn[/USER] ... 
Despite having not just ONE, but THREE different texting solutions available (eLeadCRM, CarCode w/ Edmunds, CarNow Chat & Text), I conducted this text communication using my own personal device. Allow me to shame myself before anyone else does.
I didn't even think about it, didn't have that "oh shit" moment until the very next day.
You're right. Many texting solutions are light on features and force you to use a web interface when using your phone (if it's even available) and many of those do not support MMS (pictures, video, etc.) But most of all it's due to ease and habit. Like I said, I didn't even think about it - despite the many conversations we've had right here around texting laws and TCPA.
All 3 of the texting solutions that were at my disposal are great products/features and serve their purpose well, but none of them would have allowed for the fluent text communication I had with this customer. How could they?
2 Days - but only because the customer was in the middle of travel. Which makes it even sweeter because had we not had text communication, that's a good chance the deal would have never happened.