This is totally fault of Dialog.. Because you can't get same good signals everywhere.. Dialog should'v let the customers know there are some dead spots in Service areas.. And also only few customers lucky enough to get 7.2 Mbps speed people who live close enough to Dialog towers.. So Dialog basically gave you sales tricks to sell their products without letting customers know the truth
7.2Mbps is Theoretical maximum speed of Dialog HSPA connection... So mostly it is not your actual speed.. I don't know coverage of 3G in Colombo.. but I' damm sure they don't have enough powerful towers to cover the whole Colombo... So some of you might get the speed of 2G..
And never compare HSPA to SLT ADSL.. because they r two different service types.. And both has ups and downs depending on your use & area..
for example if you live more than 3Km away from the Telephone exchange your ADSL service will suck.. So most ISP won't give you ADSL if you live over 3Km from the exchange.. ppl who lives over 3km from the exchange might get good 3G signals for a HSPA connection..
If you have dropouts try moving your modem to some place else... If your Modem capable of plugging external antenna(Most of them don't) try that..
Also you can try a small trick by using a long USB cable to plug your modem to your PC and hang your modem somewhere like a window where you can get good reception...