I had a chance to review Urban airship developer guide. They have Push APIs that  lets us select the audience, define the notification payload, specify the device types, deliver the notification.
Authentication is done based on application key and secret. The application secret is restricted to certain low-security APIs JSON format is supported. The base URL is go.urbanairship.com Push response has push_ids, the ids are GUIDS Devices have their pushTokens. Audience selectors include device IDs, segments, location, logical operators etc and is consolidated into a single attribute.  The audience selector helps in cases such as broadcast. Scheduling is done with a separate endpoint /api/schedules.
A push object describes everything about the push, including the audience and push payload. A push payload is composed of upto five attributes. audience, notification, device_types, options and message.
Device information APIs are based off of device_token and includes information such as last registration, badge, quite time etc.
Devices don't necessarily have to be a specific platform. It can be iOS, Android etc.
The location API for urban airship is interesting. They search for a location by name but results can also be filtered by boundary type such as city, province or country. The location can be searched based on latitude and longitude as well. Specifying the boundary type with latitude and longitude such as city, postal code etc is recommended.
Device registration is done with device tokens for iOS, APIDs for Androids and Blackberry PIN
The reports API gives the number of billable users for the month, broken out by iOS and Android.
Tag API can be used for creating, deleting or updating tags for an application.