HSDPA speed is slow from a mobile device?

Question

I am calling a webservice from a mobile device using a HSDPA connection and upload speed is really slow. To upload an array it is taking about 5 minutes while with a Wi-Fi connection it takes just 10 seconds. I am using the following method.

First I am checking that connection is OK by:

    try
    {
        hwrRequest = (HttpWebRequest)WebRequest.Create(strUrl);
        hwrResponse = (HttpWebResponse)hwrRequest.GetResponse();

        if (hwrResponse.StatusCode == HttpStatusCode.OK)
        {
            bConnected = true;
        }
    }

Then I am calling the webservice by:

result = webservice.function(intput);

Am I doing something wrong? Browsing with the same mobile device is pretty good.