3.5G is a grouping of disparate mobile telephony and data technologies designed to provide better performance than 3G systems, as an interim step towards deployment of full 4G capability.
3.5g is faster than that of 3g. It based on HSDPA means means now get more speed on downloading or opening of any url than that of 3g case. 3.5g gives a speed of 384 kbps while 3g gives 128 kbps.
It is actually means HSDPA-High Speed Downlink Packet Access. Its data bearing achieved the speed of 384 kbps. with 3.5G you can download contents bit faster than a 3G.