I just bought a dell Inspiron 300 (http://www.dell.com/us/p/inspiron-11-3137/pd)
The strange thing is that I tried with elementary Freya beta 2 (elementaryos-unstable-amd64.20150208.iso) and it correctly detects it as:
$ lshw
...
*-network
description: Wireless interface
product: BCM43142 802.11b/g/n
vendor: Broadcom Corporation
physical id: 0
bus info: pci@0000:01:00.0
logical name: wlan0
version: 01
serial: 9c:ad:97:d6:fa:1b
width: 64 bits
clock: 33MHz
capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless
Elementary freya is suppossed to be based on Ubuntu 14.04, and I tried with Ubuntu 14.04.02, 14.10 and also a 15.04 beta but the wireless network just won't show up.
Any idea
If you go into system settings, software and updates, additional drivers should show the broadcom sta driver(aka bcmwl-kernel-source). This driver should work for your wifi
In this forum it says that the wifi wont work on live mode, but once installed it works out of the box
http://ubuntuforums.org/showthread.php?t=2244361&p=13193735#post13193735