Hope this is useful for people hunting through old but well named topics.

This works

declare @var varchar(max) = ' '

select len(@var)

This doesn't

declare @var varchar(max) = ' '

select len(cast( @var as text))

Msg 8116, Level 16, State 1, Line 7

Argument data type text is invalid for argument 1 of len function.

This doesn't

declare @var varchar(max) = ' '

select left(cast( @var as text) ,2)

So it seems like the trend is that you cannot do any string manipulation with text fields.

Also, this

declare @var text = ' '

Msg 2739, Level 16, State 1, Line 2

The text, ntext, and image data types are invalid for local variables.

Even more reason to get rid of TEXT, NTEXT etc.