Cheaper to call US than home?

I was looking at a post on Lifehacker about using the Jott speech-to-text service to add notes to Evernote or events to Google Calendar, and apparently it is cheaper for me to call a US number from my mobile than to call my house. The flat international rate quoted on the Vodafone website is 15c per min, the rate to Irish landlines vary by time of day and priceplan  from 29c to 45c.  Go figure.