Apple has confirmed in the iPhone FAQ section on its web site that the micro-SIM from the iPhone 4 cannot be used in the iPad.
An iPhone 4 micro-SIM inserted into an iPad will detect that it is not in a smartphone and will not work, according to Nick Wilkins, press relations manager at O2.
"The micro-SIMs for the iPhone are set up to allow voice calls, SMS messages and data functionality, whereas the iPad micro-SIM is provisioned to allow pay-as-you-go data transfer only," he said.
"The two devices are designed to give a different experience. The iPhone 4 is for regular use, whereas with the iPad we offer more flexibility over data use. "
Some consumers may not welcome the news, especially as they may want to carry over a data allowance from their iPhone to the iPad.
O2 said that it will make available a SIM which can be converted back and forth between the micro and regular sizes.
The European Telecommunications Standards Institute oversees SIM cards, and there are three recognised sizes: full, mini and micro. There is no difference in the circuitry, just in the size.
Apple was contacted by V3.co.uk to ask why the iPhone 4 micro-SIM will not work in the iPad but had not responded at the time of writing.
Apple announced SIM-free iPhone 4 prices earlier today.
Kicking Palantir off of AWS is among their demands, too
Rafaela Vasquez was watching The Voice at the time of the crash, new evidence shows
PUBG price slashed on Steam after selling more than 50 million copies - as daily player numbers plunge
Use the same password for every website? It might be time to change them all