ASP.NET web services and Blackberry -- need assistance with returning complex data

I need to transfer a significant amount of structured data that goes something like this in XML -

<person>
 开发者_JS百科   <fname></fname>
    <lname></lname>
    <DOB></DOB>
    .
    .
</person> 

Each person record has 5 fields, and each time the app is opened, about 30-40 (possibly more) person records will be loaded.

Will XML be a good implementation to do this? Should I be worried about Data rates over 3G / Processor speed / Code and memory size?

Should I be looking at JSON? If so, can I make an ASP.NET web service return JSON data?

In my experience it has been very easy doing JSON parsing (and generation) in BlackBerry using the http://www.json.org/java/org.json.me.zip code, which works great and has a very small footprint. If you do want to go the XML route, check out http://kxml.sourceforge.net/ as I've seen it mentioned here on Stack Overflow before in regards to BlackBerry XML parsing.