There is no question mobility hits the nail on the head as an issue for the AEC space. Cloud (see cloud definition post) is driving it and as a result the primary distinction here is if you have internet connectivity or require a disconnected state. This is the entry question to all others because it weighs heavily on your options. Either way, the connectivity gap is closing as the 3G, 4G and beyond come to fruition but there are still those tight spots on the remotest job site or in basements that struggle with connectivity. With internet connectivity users can leverage many more options via solutions like Citrix receiver clients which are available for most operating systems and devices. This enables use of any application leaving the reality of the form factor up to the user. In addition, connected users can leverage all of the disconnected capable applications as well. This would include all your applications being marketed as "XYZ Mobile" like the offerings from Oracle Primavera and Meridian Systems which include various operating system specific applications for Windows and iOS based devices. Android seems to be the laggard OS of choice among developers.
Along the lines of applications, some great things are happening in the AEC space. Beyond The extensions of existing line of business applications (like noted above) there is a nice community of 3rd party developers that are beginning to be able to add value as business application vendors get cloud capable. Remember cloud does not mean hosted. If you refer to NIST definition of cloud, I'm simply referring to the self service and programmable characteristics. Line of business application vendors that make their applications openly (key point here) accessible via technology like web service API's enable a community of developers to work with their community.
Among laptops, tablets and phones, tablets seem to be the sweet spot as a form factor for size, weight, and visibility. The ones with good touch controls introduce a completely new experience for us adults that learn visually or have big fingers. I've been using an iPad since its first launch, and write this blog using one. Trust me, it's great.
In case you were unsure about the tablet revolution...here's some more back up via a nice white paper.