We are looking for a way to have task-level communication, so that a group of users can have a communication thread that is linked to a task and for which they receive email alrts whenever it is updated. The communication/email can go to the whole team or to a specific group of team members
If you have Project Server, you can use the project sites feature which includes SharePoint task, issues and risk lists that link to the project schedule.
If you only have SharePoint or some other means of hosting a discussion (Google groups? Outlook public folders?), you could just reference a project name and task in the thread title. Investigate to make sure the system will let you customize the recipient list the way you want so that subscribers don’t get too much e-mail that is irrelevant to them.