Try something like this:

iif(isnothing(Fields!carrier.Value),"","Carrier Name is: " & Fields!Carrier.Value)

and for the second one:

iif(isnothing(Fields!Carrier.Value),"Nothing",IIF(Fields!carrier.Value like "%Sprint%","Sprint/Nextel",Fields!carrier.Value))

It's converting to a unique identifier because the VARCHAR field needs to match the UNIQUEIDENTIFIER field. I get an error message if it's not converted. (The guys who...