Soon you could be keeping your mobile phone in your purse or wallet alongside any banknotes you are carrying.

Designer Stephen Forshaw has developed a wafer-thin phone stuck on to paper that can be used to make one call.

Mr Forshaw speculated that the phone could become a novel alternative to greetings cards.

The design has already won first prize in a competition sponsored by Sony.

Wedding ring

Dubbed the PS Call Me, the device squashes all the electronics for a phone into a flat computer chip that is thin enough to stick on a piece of paper and post, just like a letter.

And just like a normal phone, the recipient of the device contacts the sender by pressing the call button on the flat phone. The sender would activate the gadget to ensure it rang the right person.

Another disposable phone, but one made of cardboard

Special messages for family members or proposals of marriage could be recorded to ensure they were heard, said Mr Forshaw.

Mr Forshaw said the greeting-phones could sell for up to �10 each.

"The phone adds value to communication," he said. "It will be like receiving a parcel, but you can respond. It really packs the meaning in."

As well as being used to send greetings or congratulations, the phone could also be used to check that a parcel has been delivered or to ensure that children or other at-risk groups can make emergency calls.

The PS Call Me is not the first disposable phone to be invented.

American inventor Randice-Lisa Altschul has developed a cardboard throw-away phone that works until its battery runs out.