1) I was wondering how many vendors and application designers are looking into using / supporting the SMAP protocol.
We use SMAP in our product. It is an ESME client that uses SMAP for internal message transmission over MSMQ. It also acts as an SMAP-SMPP gateway.
You can see more details at http://www.startcorp.com/
including a free trial download.
2) In my opinion the current spec is very hard to follow. It lacks examples of complex messages, and there are too many hierarchy levels in the elements, which makes it hard to follow what goes where.
Many times we found the level of hierarchy quite complex to navigate. The API library we build includes many short cuts for creating elements.
Hopefully the new MMAP drafts will be an improvement (I have not had time to review them yet).
3) It would be nice to see some implementation guidelines.
4) I haven't found any references to the support of concatenated messages (The sar parameters in SMPP).
We have limited ourselves to single messages in our application (max 160/70 chars).
I have been able to successfully send concatenated messages using User Data Headers, e.g. for sending ringtones/logos. It was quite messy however.
Note that SMAP/MMAP doesn't have a character limit like earlier versions of SMPP do (later versions of SMPP can now have much larger messages in, say, Message Payload -- but it would not be supported by all SMSCs/handsets).