I just bought this, and its already really handy!
there are multiple calls/songs for each bird, most of which describe what the call kind of means ( like if its an alarm call/ mating call). not every single bird has a call tho.
The pictures are very clear and accurate as well. One of my favourite parts to this app is the comparison. you can select any two birds and compare the way they look and their calls on the same page. its a very useful field guide!
The layout is very easy to use. You can either browse birds alphabetically or taxonomical order, or you can search birds by their features, location and type all on the same screen.
there is anther feature that lets you keep record of which birds you have seen, pretty neat!
I think the only problem is that I cant use (obviously) it if my phone dies out in the field, and iPhones seem to die pretty fast when an app is being used.
I cant wait to get out and use it more!
Itachi is boss about The Sibley eGuide, v1.7.1