Via @wharlie from this deal, Vodafone is currently having 10% off prepaid mobile. Here is their list of phones however some phones were excluded there. To get Sony Xperia sola for $179 you'll need to got to its plan page and then click on "Prepaid" tab (next to 12/24 months). If you choose 365 days you don't need to buy any recharge.
See full specification on GSMArena:
- 3.7" 480x854
- Quad band 850 / 900 / 1900 / 2100
- NovaThor U8500 (dual core 1GHz + Mali-400 MP GPU)
- 512MB RAM + 8GB internal storage
Other cheap phones that are on 10% off:
- Huawei Ascend G300 (4" Android 2.3 upgradable to 4.0) — $134
- Samsung Galaxy W (3.7" Android 2.3) — $179
Note that these are locked to Vodafone network and it's $25 getting them unlocked from Vodafone (unless you found some other ways). Edit: According to Whirlpool that you can get unlock code for free.
According to this thread, about half way down, you can unlock through Vodafone for free.
http://forums.whirlpool.net.au/archive/1998188, comments from unity1 and zelda707.
I have not tried it myself.