You need to send there just a HTTP request as SOAP works over HTTP. For example via CURL it would be like this:
curl 10.10.10.10:1234/onvif/device_service -d '<s:Envelope xmlns:s="http://www.w3.org/2003/05/soap-envelope"><s:Body xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><GetSystemDateAndTime xmlns="http://www.onvif.org/ver10/device/wsdl"/></s:Body></s:Envelope>'
As a result you will get something like this with some headers:
<tds:GetSystemDateAndTimeResponse>
<tds:SystemDateAndTime>
<tt:DateTimeType>Manual</tt:DateTimeType>
<tt:DaylightSavings>false</tt:DaylightSavings>
<tt:TimeZone>
<tt:TZ>MoroccoStandardTime0</tt:TZ>
</tt:TimeZone>
<tt:UTCDateTime>
<tt:Time>
<tt:Hour>10</tt:Hour>
<tt:Minute>5</tt:Minute>
<tt:Second>35</tt:Second>
</tt:Time>
<tt:Date>
<tt:Year>2014</tt:Year>
<tt:Month>3</tt:Month>
<tt:Day>14</tt:Day>
</tt:Date>
</tt:UTCDateTime>
</tds:SystemDateAndTime>
</tds:GetSystemDateAndTimeResponse>
And also dont forget that most of the actions requires authorization headers included in to the request.
AUTHENTICATION
In ONVIF Application Programmer's Guide on page 35 is described how auth is done. For example it looks like this:
<s:Header>
<Security s:mustUnderstand="1" xmlns="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd">
<UsernameToken>
<Username>admin</Username>
<Password Type="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-username-token-profile-1.0#PasswordDigest">MuMnyh3wTxGWOCc=</Password>
<Nonce EncodingType="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-soap-message-security-1.0#Base64Binary">8Qqve9KCkNhQAAAAAAA==</Nonce>
<Created xmlns="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd">2014-03-04T14:03:05.130Z</Created>
</UsernameToken>
</Security>
</s:Header>