SMS delivery from regular phone numbers is rate limited by the carriers. Tropo throttles you to 10 messages per minute to keep inside carrier guidelines.
From a shortcode, there's no limit. And Tropo's connected directly to the SMS carriers, so you can deliver at a significant rate.
We don't provide delivery confirmation of SMS today. That's coming soon however. One thing to keep in mind, though, is that delivery can only be confirmed to the carrier. Handset delivery receipts are flaky at best. Not all handsets support sending delivery receipts, those that do often allow the user to disable it, and some carriers will block the receipt.
We have phone numbers in about 280 area codes and 41 countries. Not all of the area codes are available in the UI yet, so if you need one and don't see it, send an email to support and we'll hook you up.
(a) Speed of SMS deliverability (# of SMS that can be delivered per minute)
(b) Confirmation of SMS (i.e. can we be sure that the SMS was indeed delivered)
(c) Availability of phone numbers in different area codes