Why is Airdrop not available between iPhone and old MBP

Solution 1:

Your MacBook Pro does not contain the necessary hardware to support AirDrop.

In OS X, the feature didn't use Bluetooth, instead using Bonjour and personal area networking over WiFi to discover and transfer files between Macs.

When iOS gained the feature in version 7, it was a completely different implementation, using Bluetooth LE and WiFi Direct. That's why it was not previously compatible with the OS X implementation.

Apple has now retrofitted the iOS implementation onto OS X in Yosemite. This in turn requires a chip for Bluetooth v4 and LE support. This chip was not included in MacBook Pros until mid-2012.

You may be able to replace the Bluetooth chip in a 2011 MacBook Pro. See this thread on MacRumors. It references Handoff/Continuity but the underlying chip replacement is what is needed to enable AirDrop as well.

As it turns out the 2011 MacBook Pro can use the same Airport/Bluetooth card as the mid 2012 Macbook pro and its user replaceable so by replacing the 2011 macbook pro Airport/Bluetooth card you should have the ability to use Handoff/continuity.