Some Verizon Wireless customers complained they were unable to buy its iPhone online, but the company said sales were mostly running smoothly on its first day of Internet orders for the long-awaited phone.

The No. 1 U.S. mobile service started taking online orders for its Apple Inc iPhone at 3 a.m. EST on Thursday, a week before it is due to hit its store shelves. Verizon Wireless had said it was preparing for heavy demand.

Spokeswoman Brenda Raney said the company was pleased with how the online system had performed and that the majority of customers have been able to process their orders with no problems. However, this was not the case for everybody.

We are aware that some customers have received error messages and we are working through the issues with the individuals to ensure they get their order placed, Raney said.

Verizon's launch of online sales ended AT&T Inc's more than three-year hold on U.S. operator distribution of the popular device.

When AT&T and Apple launched pre-orders of the iPhone 4 in June last year, heavy demand caused technical problems on both companies' websites.

Some analysts said Verizon Wireless could sell as many as 13 million iPhones this year. Verizon's earnings guidance for the year assumed sales of 11 million iPhones, as this was in line with the average analyst estimate.

While Verizon Wireless had said it would have a limited stock of phones for its first day of sales, Raney said at 10 a.m. in New York, that Verizon still had no issues with inventory.

GOOD BUT WITH TRADE-OFFS

While many of AT&T customers are tied into contracts, analysts still expect some to leave for Verizon due to AT&T's reputation for poor network performance, particularly in cities like New York and San Francisco.

The first reviews of the new device, which came out on Thursday, said the Verizon Wireless iPhone voice service worked better than the AT&T iPhone service. They noted that switching from AT&T would come with some trade-offs.

Wall Street Journal reviewer Walt Mossberg said that while the Verizon Wireless iPhone had fewer dropped calls than AT&T's, the Verizon Wireless Web surfing speeds were slower than those experienced by AT&T's iPhone.

New York Times reviewer David Pogue said he was impressed the Verizon Wireless iPhone made calls in his house, which he described as The Cellphone Signal Torture Chamber of Doom.

But unlike AT&T's iPhone, the Verizon Wireless phone does not allow simultaneous Web surfing and voice calls.

If you receive a call while Web surfing in Verizon's 3G network coverage area, the online session is interrupted so you can answer the phone, but if you are in an area with a slower 2G connection, the call goes directly to voicemail, Pogue said.

The Verizon iPhone may also frustrate some business travelers as it works in far fewer countries than the AT&T iPhone, which supports a more widely used network technology.

Verizon Wireless is a venture of Verizon Communications and Vodafone Group Plc.

AT&T shares were up 12 cents, or 0.4 percent, at $27.79 on New York Stock Exchange, where Verizon stock slid 6 cents to $36.10.

(Additional reporting by Jonathan Oatis; editing by Dave Zimmerman and Maureen Bavdek)

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