No, that's not an Embraer plane or Mercedes car. It's a Huawei modem.

Long story short: I had an E220 locked to 3 UK, which worked fine. After forgetting it in a hotel room in PRG, and despite them having found it and keeping it till I come back, I decided to buy an unlocked E172 so that I could use it with other SIMs abroad as well as not having it hanging off the laptop (the E172 is a USB stick). This works fine but it really buggers the sims I put in...so after a week or so, my connection will start getting broken every half an hour or so. It reconnects and works fine until it breaks again and so on...it gets worse and I need a new sim by the time my 30-day allowance is running out (by then it's breaking every 3-5 mins). They're free but this whole saga is a PITA.
Anything I can do to reduce wear? I need the connection most of the day, so turning it off isn't a great option...

Wear? I've never heard of a sim card "Wearing out". Dropping connections doesn't sound like a sim card problem, it sounds more like an account issue.

Sims either work, or they don't. If I were you, I'd look for a different culprit.

"Sim cards" are also the number one thing operators blame when they can't fix an issue. There are only a few things that can kill a sim, incorrect pin codes, puk codes or using it in a sim cloner will kill it, not using it in a USB modem. When a sim dies, it's gone for good. If the USB modem "wears the sim out", it's a physical thing and it would involve actually damaging the gold plated contacts on the card, but even then the sim would either work, or not work. Replacing the sim every month won't fix this, replacing the modem will.

I constantly swap my SIM cards and never have worn one out. My UK SIM is from 2001 and is swapped in and out all the time and is just fine. Could it be a voltage problem in the design of the modem?

But that is exactly what happens! After 3 weeks' use, my sim looks like it's been attacked by some rather vicious cat claws!!

can you take a pic of this?
Sounds like some damage/foreign object in your modem

Get a new modem... Sounds like the sim reader is broken.

grr...100 quid down the drain- that one I'd bought (brand new in box) from ebay and, even if I don't doubt the good intentions of the seller, I can't see any way of getting my money back...

Are you handy? Open up the device and see what is causing the damage. It could be as simple as bending a small piece of metal so it doesn't scrape your card.

Well, I haven't got much to lose so I'll give it a right go tonight!

I can't seem to open the bloody thing up...