This is not necessarily a Switchvox only issue. This issue actually stems from the fact that pecl now installs pecl_http v2 instead of v1.
Apparently since moving to v2, you need to reference the namespace such as (http\Env, http\Encoding, http\Client, etc)
If you have already installed v2 version of pecl_http, then you need to first uninstall it using:
pecl uninstall pecl_http
To force install pecl_http v1:
pecl install http://pecl.php.net/get/pecl_http-1.7.6.tgz