Tone Dial is a simple app that dials your iPhone contacts as DTMF tones through the speaker of your iPhone so that you can call using your land line.
Place the speaker of your iPhone next to the microphone of the land line phone and dial contacts from your iPhone on your land line.
Tone Dial includes several options to "adjust" the numbers in your contacts to work correctly over the land line. For example it can convert numbers starting with "+" into country exit codes so that international calls can be made correctly. It also has options to add or remove "1" from numbers outside your local area code.