The process of calling someone from a cell phone and having another number show up in the caller ID is called Caller ID spoofing. This practice is now illegal in the United States.
Spoofing services would give users the ability (for a fee) to enter the number they wished to call, their own number and the number they wanted to appear on the caller ID. The source number would be called first, then once answered the destination number would be called and bridged together. A lot of these providers also offered the ability to record calls and change the voice.
In February 2010, the Truth in Caller ID Act of 2009 was passed, President Obama then signed the bill to make it law in December 2010. The bill makes it illegal to "cause any caller identification service to knowingly transmit misleading or inaccurate caller identification information with the intent to defraud, cause harm, or wrongfully obtain anything of value”. The only exemptions are blocking your own caller ID on outgoing calls, and law enforcement.
However, despite this law, there are still companies operating Spoof caller ID, including www.spoofcard.com/ They claim that as long as you are not using their service in violation of the law with the intent to "defraud, cause harm or wrongfully obtain anything of value”, then caller ID spoofing is still perfectly legal.
In conclusion it still seems like a very grey area and if you do sign up to one of these caller ID spoofing services, then tread carefully as you could find yourself in violation of the law.