Low cost, pay as you go mobile phone prefixes

The market for low cost landline prefixes to get cheaper international calls is well established. You just dial a prefix to your number, sometimes it tells you the cost, and then connects you, billing you over your provider.

Does such an option exist in Germany, or indeed any other country for mobile phones. A prefix that will give you a cheaper call from your mobile?

Voipcheap provides a access number so that you can call international destinations from your mobile. But you will need credit in your voipcheap account. In addition to the voipcheap charges, you will be paying the normal mobile charge to call a landline. I have not yet tried this option, but looks OK.
http://www.voipcheap.com/en/newsflash.html#news2

Thanks for that Minga. Doesn't really help me as I'm looking for something without signup.

In that case, you can try a "Call-Through" service like "TeleStunt". Call tariffs to 0180x numbers are standard.

EDIT - This is not that cheap as my mobile provider charges 69 cents/minute for calls to 0180x numbers.

If you want something without sign-up then there is none, as there is no mechanism to charge you back through your provider. It only works with landlines because of a crazy quirk in the German Telecommunications rulings that require Deutsche Telekom to handle incoming charges from alternative providers and pass them back to the customer. I don't believe there is any parallel with any other provider, or for that matter in any other country. There are plenty of pre-pay callthrough accounts where you pay into a credit account then call a landline (or 0800 free) number then call on to the mobile or international number you want and thereby deduct against your credit. You could also use something like Tarifhunter (only on smart- or java enabled phones) to hunt out least-call routing methods...

Telestunt is interesting. But how much does it cost to dial a 0180 number?

Tarifhunter is a Java or Symbian application, but it doesn't seem released yet.

Calls to 0180x numbers depends on your provider. 3.9 cents/minute from fixed lines, 69cents/minute from O2.

Yes, I've just found out that T-Mobile, my provider charges 49 cents per minute. A bit cheaper than an international call I guess. Must try it out.

You can download it here
Another alternative (and one I use) is to use ISDN or VoIP services in your home and dial through the home router. I dial a special (home) number, get a dial-tone at home then dial on using call-by-call to my international destination. That way the call costs as much as a call home, plus a cent or two a minute

What about calling cards. Can you buy a scratch card, call a special number, enter your PIN and make cheaper mobile phone calls.

You certainly can for landlines. I've used the landline cards and they're the cheapest way of making non VOIP calls. I think I've seen mobile cards but I've never worried about them because I use landlines as much as possible.