Someone way back when I worked in the electronics department at K-mart joked with me while I showed him cordless phones that the most expensive word in the English language was simply "Hello" (not goodbye because lots of people hang up on each other in disgust).

I think the trend has changed now that landline phones are pretty much flat rate, and cell phones are for the most part, somewhat metered.

So, I think it's a most expensive sentence now.

I think the most expensive SENTENCE (besides "Iraq has WMD's") is:

"Sorry -- I lost reception on my cell phone."