Both are QWERTY keypad phones that are available with all multimedia options that will keep you satisfied. The Omnia is a slightly more costly phone but provides more features too. It is powered by Windows Mobile 6.5 O S as compared to Samsungs own proprietary OS on the Chat 335.
Some common features in both are
GPRS and EDGE connectivity for 2G Network
Stereo FM radio with RDS
2.4 inch Display
PC Sync with USB
2 Mega Pixel Camera
Audio and Video Playback and recording
However the above mentioned features do vary a lot in their Version numbers. For example, Samsung Chat 335 has Bluetooth 2.1 in comparison to the Bluetooth 2.0 in the Samsung Omnia 652 and the Java in chat 335 has MIDP 2.1 as compared to the MIDP 2.0 in Omnia 652.
Samsung Omnia 652 cannot be written off just because it has a few features that do not have the latest upgrades. It has its own advantages and features that you will not find in the Chat 335. The best example for that is the 3G connectivity that the Omnia 652 provides. The phone supports high speed internet access and data downloads for up to 3.6 Mbps.
The Omnia 652 also has GPS support that will come in handy during long trips down the country side. The Omnia 652 has a larger internal memory of 220 MB as compared to the mere 54 MB of the Chat 335 and the Omnia 652 has external memory support of up to 16 GB whereas the Chat 335 has support for only up to 8 GB.
On the battery backup section the Samsung Chat 335 pips the Omnia with 14 hours of talk time support and up to 620 hours of standby when compared to the 12 hours (2G), 7 hours (3G) and 600 hours standby time in the latter.
Thus both the phones are excellent value for money phones. With regards to the price, Samsung Chat 335 is the cheaper choice at Rs 4750 but at Rs 7000 the Omnia 652 provides enough and more features to justify its higher price tag.