Besides the use of Lotus Notes(LN) in connection with a Blackberry(BB), one could also connect the BB, and so also LN with "Remember-the-Milk". This can be done by installing the "Milk Sync for Blackberry" on your BB Device.
This BB application is available free of charge for RTM pro users (25$/Yr) for download on the RTM page. It keeps the genuine BB Task Management App and the RTM Web-App in sync and since this works seamlessly, you could at least have all your to do's on you BB on your Work Computer and on your i-device in an unisense sync as well.
Unfortunately the RTM sync only works with lists and not with tags.
A workaround might be that you create smartlists for the regular tags you use (Tag:@phone) and save them for automatic update.
This could cause some inconvenience, so you better double-check wether you‘re fine with it before you make use of this hint. In addtition you should check on using the same tags in the LN environment and the RTM environment, so you dont cause duplicates or confusion.
As a hint you should try to find out, wether a tag related smart-list in RTM helps you solving part of your Problems.
Maybe you decide to only sync the work related task into you notes environment like I did.
As you will have found out, this work around helps you connecting BB, Notes, RTM and iDevice, so you can have all to do's in sync on all devices.
Maybe in the near Future we will have tags sycing as well so all works together seamlessly.