what version are you using? I think that request is not available from 8.x ?

Anyway, you could use listRoutePlan and use dnOrPattern (i.e. 55*) and type in the searchCriteria

you cann try to use the axl method "executeSQLQuery" with the parameter

<sql>SELECT numplan.dnorpattern AS numplan_dnorpattern FROM numplan WHERE numplan.dnorpattern LIKE '55%'</sql>

 
Rocco,
The ListRoutePlanReq is just performing a SQL query for you. When it ask for the dnOrPattern use the SQL pattern i.e 55% would return 55 and anything after that. This is also true for type and partition. i.e if you have a partition name "MyPT" and you search "My%" it would return "MyPT" You can also flip these around and use %55 which would return 12355. You can even do %55% which would return 125534. Hope this helps!

Is listLine available in 7.x?  I have been working in 8.6 so not paying attention to older ones. 
 
listLine allows wildcards (oddly the % sign) so:
<ns:listLine sequence="?">
    <searchCriteria>
        <pattern>55%</pattern>
    </searchCriteria>
</ns:listLine sequence="?">