Hemant Sutar of Chembur had been waiting to activate 3G service on his iPhone.

He hoped to use his phone as a modem and power his iPad with 3G speeds.

This Vodafone 3G customer from Mumbai had signed up for the operator's service on a trial basis to experience faster, smarter and better speeds.

But what he received was not what he had expected.

As soon as he activated his 3G connection, his 2G network failed and for the next few hours he could not make calls.

The customer care section, duly informed him that the operators were still facing technical difficulties.

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"After that, I had 3G network for only two hours. Later, that too, disappeared. I was told there was no 3G network in Chembur area, where I live and work," he says.

A fluctuating 3G network is a common complaint from consumers who are early adopters of the service.

Users say their new 3G network keeps shifting back to 2G network, mostly in the middle when they are downloading or uploading a video. For the time period that networks shift from 3G to 2G, customers are unable to make calls as well.

The companies are defensive. Vodafone Essar said they had not heard any such complaints.

"If there are any such cases, these are mere aberrations and we expect it to get sorted soon," the company said.

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Bharti Airtel did not respond to a query on network issues.

"About six out of 10 times, when I try to surf the network it keeps saying 'network error'. The speeds are much better in the night. When I am at home in the night, I would rather surf on my laptop from the landline connection," says Snehal Vaidya, another 3G user from Mumbai.

Rahul Kamath enjoys the ultra fast 3G speeds which are 10 times than that of his 2G GRPS plan.

But, this Airtel consumer is still on the free trial period till the end of March and is undecided about shifting to 3G.

"It is very expensive," he says.

The fluctuating network is frustrating as well.

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"Sometimes a video gets uploaded in a matter of minutes, sometimes it would just not upload. The customer care always has a standard answer, 'we are updating our servers'," laments Kamath.

And 3G service is not living up to its most luring promise -- entertainment while on the go. On the contrary, customers in Mumbai says the 3G network doesn't work while travelling in the trains.

"The advertisements say that 3G users need not miss matches and watch TV on mobile.

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But once we get on to the train, there are no traces of network, neither 2G nor 3G," says yet another frustrated subscriber.

Experts say these issues will be the deciding factors before customers start using a premium service like 3G.

"Even in a metro like Delhi, the 3G signals are weak. Consumers are unable to enjoy the high-speed internet on the move. Quality coverage is not available across the city. "Roaming is a main concern for 3G users.

"Operators should invest more in infrastructure to ensure quality of services," says Baburajan K, chief editor, telecomlead.com.