Why nobody use "search" of the forum, or at least google?
However, this is a "tricky" thing to do, since that in iphone there aren't framework to help you on consume webservices. So you should be able to create your xml to send in http post to your webservice with your data in input, and then you will receive an xml as output, that you need to parse manually. A real boring thing if xml have many items\subitems.
There are really many (too?) threads that ask about it on the forum, a good summary is a my post here:
http://www.iphonedevsdk.com/forum/ip...lp-needed.html
and since that you want to use an asp.net webservice, look also here
Consuming ASP .NET web services in iOS part1 | .NET
but since that webservice is a standard based on soap, there isn't a real difference.