[inquisitor]

I understand, that you run the wget command locally (i.e. on your linux machine, which is connected to the internet via the named providers).
Proceeding on this assumption the problem appears pretty simple. http-applications do always send the so-called USER_AGENT parameter revealing it's identity with each http-request.
When you use wget the http requests sent to the server (and passing the network operator's proxy) will contain the USER_AGENT "wget 1.9.2". The proxy will so identify the request as not coming from a handset and so will block it.
What you need to do now, is faking the USER_AGENT. Therefore simply set the user_agent parameter to some mobile phone when executing wget. In the following example you will send the (pretty long) USER-AGENT of a Nokia N95 with your request:

wget --user-agent:"Mozilla/5.0 (SymbianOS/9.2; U; Series60/3.1 NokiaN95/11.0.026; Profile MIDP-2.0 Configuration/CLDC-1.1) AppleWebKit/413 (KHTML, like Gecko) Safari/413" http://www.poseidon.hcmr.gr/images/m...db09082515.png

That should do the job.

Depending on which user_agents are blocked by the corresponding operator you could also use the user agent of a desktop browser like Firefox, which would look like this:

wget --user-agent:"Mozilla/5.0 (Windows; U; Windows NT 5.1; en; rv:1.9.1.2) Gecko/20090729 Firefox/3.5.2 (.NET CLR 3.5.30729)" http://www.poseidon.hcmr.gr/images/m...db09082515.png

For details on wget parameters, check the documentation: http://www.gnu.org/software/wget/manual/wget.html