Installation of dependencies:

yum install php-channel-aws.noarch php-channel-guzzle.noarch php-symfony2-EventDispatcher.noarch

Installation of the library itself:

pear install aws/sdk

Checking:

[root@robo ~]# pear info aws/sdk
ABOUT PEAR.AMAZONWEBSERVICES.COM/SDK-2.2.1
==========================================
Release Type PEAR-style PHP-based Package
Name sdk
Channel pear.amazonwebservices.com
Summary Official PHP SDK for Amazon Web Services.
Description The AWS SDK for PHP enables PHP developers to
easily work with Amazon Web Services and build
scalable solutions with Amazon S3, Amazon
DynamoDB, Amazon Glacier, and more.
Maintainers Michael Dowling <[email protected]> (lead)
Jeremy Lindblom <[email protected]>
(developer)
Ryan Parman <[email protected]> (developer,
inactive)
Release Date 2013-03-18 17:30:25
Release Version 2.2.1 (stable)
API Version 2.2.1 (stable)
License Apache 2.0 (http://aws.amazon.com/apache2.0/)
Release Notes This release adds convenience features for the
Amazon S3 client, updates the Amazon RDS client
to use the latest API version, resolves an issue
with the Amazon EC2 client, and includes support
for additional regions and other enhancements.
Required Dependencies PHP version 5.3.3
PEAR installer version 1.4.0 or newer
Package guzzlephp.org/pear/Guzzle
Version 3.0.3 or newer
Extension curl
package.xml version 2.0
Last Modified 2013-04-16 16:10
Previous Installed - None -
Version
[root@robo ~]#

Getting list of installed files (there are a lot of them):

 pear list-files aws/sdk

Upd.
If it doesn’t work for you, try this way:

pear -D auto_discover=1 install pear.amazonwebservices.com/sdk