Firstly, this is a great contribution, and really adds to the usefulness of our shop.
I've been using the RM module for some time, without any problems, and have just added the Business Post (due to the fact that RM are getting worse at delivering stuff every day!), and have found a couple of small problems:
1) My tracking numbers are 14 digits long (which I sorted out)
2) The module works fine for items that are delivered and in transit, but doesn't return any information for parcels in 'other' states (i.e. not booked into BP's server). from my experience with the RM module, this is because the site is returning info that is not understood. However, I can't figure out what!
Try: 30542020000087 for an example.
Suggestions etc. welcomed!
Also, a suggestion for a mod. (which I will probably make to my version) use a constant for the account info, (i.e. the 1st 7 numbers of the (in my case) 14 digits) and then allow the remaining characters to be typed, padding to 7 with zeros, which, when added to the end of the A/C number will make 14 digits.