The following devices have been tested with Viber:

ICS: Is momentarily only fully supported on the below mentioned ICS devices.

Jellybean: Is compatible with Viber version 2.2.1.21 and up.

Alcatel OneTouch 997 (Viber 2.3.5 and up)
Alcatel OneTouch TCL S600 (Viber 2.3.5 and up)
Alcatel OneTouch 8008X
HTC ChaCha
HTC Desire
HTC Desire HD
HTC Desire S
HTC Desire Z
HTC EVO 3D
HTC Incredible S
HTC Legend
HTC One X/S
HTC Nexus one
HTC s720e one x
HTC Sensation
HTC Sensation XL
Gionee CTRL V2
Google Nexus 4
LG Optimus One
LG Optimus 2
HTC Wildfire S
Motorola Defy with Motoblur feature
Motorola Milestone
Motorola RAZR
Orange San Diego(Intel)
Samsung Galaxy ACE
Samsung Galaxy Europa
Samsung Galaxy Note
Samsung Galaxy Note 2
Samsung Galaxy Nexus 
Samsung Galaxy Mini GT-S5570
Samsung Galaxy GT-15500
Samsung Galaxy S
Samsung Galaxy S GT-I9000
Samsung Galaxy S 2
Samsung Galaxy S 3
Samsung Galaxy Y(Partially supported with calls on 2.3.5 and up)
Samsung Galaxy Y Duos(Partially supported with calls on 2.3.5 and up)
Samsung GT-i5510T
Samsung Nexus
Samsung Nexus S
San Diego Intel
Sony Ericsson Xperia ARC
Sony Ericsson Xperia X8
Sony Ericsson Xperia X10i
Sony Ericsson Xperia X10 mini
Sony Ericsson Xperia X10 mini pro
ZTE Blade

ICS:
Samsung Galaxy Nexus with ICS
Samsung Galaxy Nexus S with ICS

Jellybean:
Compatible with Viber 2.2.1.21 and up.

Problematic devices:
HTC Hero
HTC Wildfire

* Other devices: Devices not listed or Android Tablets are only partially supported, Or not supported at all.

Custom ROM:
At the moment we do not support custom ROM.

Stay tuned!
Visit us on Facebook and Twitter:
http://facebook.com/viber
http://twitter.com/viber