I sipped my drink and listened in a desultory fashion to my companions' conversation going on around me. The topic (the football championship) did not interest me at all. I found myself wondering about the origin of these messages. It seemed to me that no-one ever seems to create these jokes; no-one types them in, laboriously keying in their own imaginative thinking for the amusement of their friends and acquaintances. Invariably, they are forwarded from someone else: a mate, a colleague at work, that bloke in the pub, even family members - I know that my wife gets a surprising number from her mother.

Unlike messages from most people I actually knew, these joke messages are generally properly spelled and self-evidently written to be comprehensible to anyone with a reading age of six - exactly the target audience specified for journalists working for those red-top tabloid newspapers. Oh, there is often a liberal sprinkling of rude words - perhaps more than a time-served curmudgeon like myself would really like - but the general impression is one of a careful, even professional standard of writing.

By this time, my companions' conversation had moved on to the even more boring topic of politics, comparing the reputation of the current Prime Minister, in power unelected and with his reputation for financial prudence apparently in tatters, with the previous one whose reputation seemed to be holding up well. A masterful example, I considered, of that old adage: get out while the going is good. I ignored their chat.

Now, forwarding on text messages costs money. Oh, not much, of course, and it may even seem like it is free, if you have a "500 free texts" tariff - or whatever - included in your monthly fixed charges. Sending on all those jokes means that you feel that 500 text messages a month is a necessity, rather than a luxury, and worth paying for.

This was not the first time that I had wondered whether the whole text message joke thing was a scam, a deliberate attempt by the mobile phone companies to increase the traffic on their networks and therefore their revenue. I knew that the incremental cost of handling an individual SMS message is effectively zero, since this is entirely automated. As is so much in the modern world, the price of this service - to the punter in the street - of sending a message is almost entirely unrelated to the cost to the telco.

All these mobile telcos are chasing the magic ARPU - Average Revenue Per User - figure which is such an important measure of success for these companies - at least, as seen by the all-important stock market analysts. Their strategy is simply a matter of charging what the traffic will bear, which is why there are so many confusing packages, deals and offers.

It would not be hard to arrange, I considered. All the mobile phone companies run numerous SMS Centres: basically computer systems that are the first hop for any new message from a phone. For there, the text is forwarded on fast optical fibre networks to the appropriate SMSC for the recipient's mobile network - which might belong to a different operator, of course, or even be in another country.

The SMSCs support a bulk sending capability made available by the telcos to companies large and small, offering a reduced cost per message, although it is definitely not free. Of course this could be used - indeed, it has been used - for the sort of aggressive bulk-mailing scheme these days known as spam. Mercifully, this seems to be less prevalent than, say, junk email, probably because, for SMS, it is always the sender who pays.

Even so, I could imagine some near-automated process, probably sited in some overseas call centre. A few people would be needed to maintain lists of subscribers to a "free joke" service, supported by a small group of talented copywriters paid to craft numerous short messages on the news of the day.

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