Hello Steve, all great questions, certainly one way to learn about each of the platforms is to have a demo account. There are some basic things to look at.
1. Where are you planning to deploy? Will it require working with multiple Operators, if so do they all support or use the same platform or do I have to do individual integrations?
2. What does my business model call for, do I need tools that allow me to monitor for exception behavior and create actions based upon those events or do I just need to turn SIMs on and off?
3. I don't think you will find detailed information about each of these platforms until you actually sign up for a Developer Kit or similar. After all, each of the companies you mention have IP they want to protect and require some level of NDA to open up the details.
4. When you talk about provisioning, and you even elude to this a little yourself, what type of provisioning are you referring too? From the platform perspective most would assume you have provided the needed APN names and credentials for accessing the network, when your device makes a request to use a service, lets say data to simplify the answer, then your device should pass those attributes along with the service request. The platform should then evaluate the status of the services like, is this service type allowed, is the SIM in a provisioning state to allow traffic etc. Where the real power of the platform comes in is not that it allows your device to connect if all of those items are correct, but how it manages that request, for instance when the device connects can it create an actionable event to trigger a business process, can that provisioning state be managed dynamically when an event happens, such as usage over a certain amount, or connecting more than twice a day? Provisioning is fundamental to all of the platforms, business enablement based upon that happening is where the differentiation starts.
Your right to be looking in depth at these platforms, you will find there is a tremndous amount of differentiation between them.
Item 3 is something I have been asked a lot by customers getting our GSM modem, http://www.icpdas-usa.com/products.php?PID=3397 . How to use the AT protocol? The easy way is, let Windows do it. The OS can handle getting internet access, 'a connection', with all the AT code.
You can get a list of AT commands that are common to all modules at M2MSupport.net. In addition to that, each module vendor generally offer extended AT commands for additional functionalities such as FTP, HTTP, Email, TCP etc..