It's all fun and games — until you can't use your phone anymore.

Two sons wanted to give their New Jersey father the best birthday surprise for him before he turned 62 on Saturday, so they decided to put up a huge billboard with a birthday message.

The sign revealed Chris Ferry's phone number, his photograph and the words "WISH MY DAD HAPPY BIRTHDAY".

Sons prank dad with giant birthday billboard, bringing in thousands of birthday messages. Photo / CBS
Sons prank dad with giant birthday billboard, bringing in thousands of birthday messages. Photo / CBS

What Chris Junior and Michael didn't expect, was that their father received over 15,000 texts, calls and Facebook messages from people around the world.

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"We thought people in the local area and his buddies would call in, and this would be a fun memory," Chris Junior told CNN. "We did not know that it was going to be like this."

Their father first realised he was pranked when he received a birthday text from a stranger.

"[I was] saying 'Nick? Nick who? You don't know me, how do you know it's my birthday?'" Ferry told CBS. "[They] saw it on a billboard."

Soon after, Ferry drove to the billboard which was outside Atlantic City and took a photo with it.

Ferry revealed he found their son's prank funny at first, but soon got angry when his phone became un-useable as messages flooded through from Germany and Africa.

"It was fun until this morning. Then I wanted to kill them [his sons]. But I'm going with it, having a good time," the dad told CBS.

Ferry received so many birthday messages that he had to change his phone number. However, the billboard will stay up for another three weeks.