Phonebooth which has been label as the "Alternative to Google Voice for Small Businesses." has released two iPhone apps to save businesses and individuals time and money. One is called Holdr [iTunes link] and the other is called Conference Starter [iTunes link].
How Holdr works:
Holdr beta waits on hold for you, so that you can get on with your life. If you are calling a number where you expect to be put on-hold (like an airline or the IRS), just fire-up Holdr, dial the number and press *7 when they put you on-hold. Holdr will call you back when they pick-up.
How Conference Starter works: [...]