US consumers’ obsession with using smartphones like iPhones, to find restaurants, surf the Web and navigate city streets helped propel a 26 percent rise in AT&T’s fourth-quarter profit — but at a cost for the operator.

The strain that wireless devices like smartphones and e-readers have placed on AT&T’s network is such that the company announced it will increase capital spending by about $2 billion this year, targeting improvements in its wireless service.

The increase was unveiled as AT&T posted revenue and earnings that largely matched analysts’ estimates, although its addition of 2.7 million net subscribers in the fourth quarter was nearly 1 million more than expected.

Profit came in at $3.01 billion, or 51 cents per share, from $2.40 billion, or 41 cents last year.

Analysts did, however, point out that just 910,000 of those were the highly prized monthly bill-paying customers, compared with bigger rival Verizon Wireless’ addition of 1.15 million postpaid users.

Every new AT&T customer puts more demands on its network.