I have finally worked out how to get my Nokia E61 to act as a bluetooth modem properly with my MacBook. There are so many contradictory instructions on the web, but I eventually got it working. I would like to thank the chaps at O2 customer services who, despite a clear policy not to support apple Macs, went out of their way to help and find any relevant information.
The first thing to do is make sure you have all the necessary settings in the correct place on your phone, below are the details for the mobile.o2.co.uk access point I set up and used:
Under Menu > Settings > Connection > Access Points
In here I created a new access point called O2 Mobile Web.
Data bearer = Packet data
Access point name = mobile.o2.co.uk
User name = faster
Prompt password = no
Password = password
Authentication = normal
Homepage = none
Then, under options go to Advance settings and enter the following:
Network type = IPv4
Phone IP address = Automatic
DNS = User defined = Primary DNS = 220.127.116.11 Secondary DNS = 18.104.22.168
Proxy serv. address = None
Proxy port number = 0
Once this is completed go to the Packet data menu under Menu > Settings > Connection > Packet data and enter the following:
Packet data conn. = When available
Access point = O2 Mobile Web (this must be exactly the same as the name you gave to the access point above)
Then, moving to your Mac enter the following details:
Download scripts from http://www.taniwha.org.uk/ (direct link http://www.taniwha.org.uk/files/Nokia3G-2006-08.zip) and install them into the Modem Scripts folder under Macintosh HD > Library > Modem Scripts.
Pair the mobile phone via bluetooth and select the option to DIAL for an internet connection (rather than direct connection).
When prompted for a Modem Script, use the one you have just installed (I understand they are all different, the one that worked for me was Nokia CID 1).
User name: faster
Dial up Number: mobile.o2.co.uk
Once you have completed this setup you should be able to use the 'Internet Connection' to dial your phone as a bluetooth modem.
Of course these are the settings for O2 in the UK so they may vary by region / provider.