Prepaid mobile phones from Simyo - Germany

I am looking at the mobile phones at this site:
https://handyshop.simyo.de/start.htm
Are these phones locked to work only with simyo? Is there any operator that
sells unlocked phones in Germany?

Many thanks

The Simyo phones are unlocked, see here: http://translate.google.de/translate?u=http%3A%2F%2Fhandyshop.simyo.de%2Fhilfe.htm&sl=de&tl=en&hl=en&ie=UTF-8

Another good source for unlocked phones is Congstar, here's the link with up to 20€ off compared to the "normal" Congstar prices: http://prepaidhandy.congstar.de/Alle-Handys---1.html?refID=8001

Advantages + Disadvantages of Congstar here: http://www.toytowngermany.com/forum/index.php?showtopic=72033&view=findpost&p=1818040

from Congstar help section, saying their phones are unlocked: http://translate.google.de/translate?u=http%3A%2F%2Fcongstar.custhelp.com%2Fcgi-bin%2Fcongstar.cfg%2Fphp%2Fenduser%2Fstd_adp.php%3Fp_faqid%3D20%26p_created%3D%26p_sid%3D9kq5YcMj%26p_accessibility%3D%26p_redirect%3D%26p_lva%3D%26p_sp%3D%26p_li%3D%26p_topview%3D1%26search%3D1&sl=de&tl=en&hl=en&ie=UTF-8

Thank you for the information. From what I could translate in the website, congstar does not have minimum fee for prepaid SIM cards. Do you know how often one needs to recharge the SIM card so it doesn't get blocked? I would like to have a cell phone to receive calls but do not plan to use it very much.

You start with 10€ credit when you buy:
- the Congstar Starter-Paket for 9.99€ (i.e. if you only buy the SIM-card), or
- the phone whose price includes the Starter-Paket (i.e. SIM card),
and if you don't use it your credit it will remain that much always.
All credit on Congstar is valid indefinitely (i.e. you do not have to recharge periodically), so it's ideal if you just want to be called.

It looks like this is exactly what I need. Thank you very much! I am trying to place an order and the starter-paket is already included in the price of the cell phone.