Since you're getting an authentication  error have you tried on an anonymous list
to rule out the mobile  aspect?

What authentication is your site  using? If it's not using Basic, try that. If
you're only using NTLM the Blackberry may not be able to speak that.

you will have to enable basic authent on WFE servers serving these lists. But
careful, that is sent at base64 cleartext and can be hacked. best practice is
using SSL in conjunction with Basic authentic.

You are correct when stating that Blackberries can't understand NTLM authentication. There are a few different solutions to your problem.

If using BIS

1) Vanessa's answer
2) Use forms authentication  instead of basic
3) Use anonymous authentication (not advised for sensitive contact)

If using a BES then
1) Enable Support http  authentication on bes under MDS-CS settings. This will allow the BES to authenticate using NTLM/Kerberos on behalf of the Blackberry device.
2) Take a look at a third party product like SilverDust (http://silverdust.softartisans.com). SilverDust is the most secure out of all listed (granted you have a BES) and formats SharePoint content in a more usable manner then the default  /m