Networks haven't been physically damaged, but airwaves are clogged as people try to reach friends and family.
The blasts hit the city the day after it was awarded the bid for the 2012 Olympics and as the G-8 summit was getting under way in Scotland. Police responded to reports of incidents at six subway stations, and at least one bus explosion was confirmed. British Prime Minister Tony Blair said in a televised statement that it was "reasonably clear" that the explosions were the result of "terrorist attacks."
In the immediate aftermath, a statement from the U.K.'s largest network operator, Vodafone, said that an excessive number of calls had caused outages. The operator consequently set aside capacity for phone calls to emergency services.
Explosion hit the city
the day after it's
awarded the right to
host the 2012 Olympics.
"Following the major incident in London today, Vodafone London switches are at capacity (which is very rare), so we're having to go into 'access overload' procedures, which means freeing up a proportion of capacity across London to ensure the police and emergency services can communicate," the company said.
The operator added the problems should be temporary: "Customers will experience temporary issues making calls, but we urge them to keep trying."
The Orange network is also experiencing difficulties, a company representative said.
"We can confirm that, due to the number of high calls currently being made on the Orange network, some of its customers in London may experience difficulties making calls on their first attempt and may have to try several times before they get connected," the representative said.
The problem is affecting the London area most severely, the representative added, but other areas will experience problems as well.
As for O2's network, a representative said the operator is working to overcome problems.
"The O2 network has not sustained damage due to the explosions in London today," he said. "The network is experiencing some congestion in affected areas due to the high volumes of calls. Steps have been taken to increase network capacity."
T-Mobile also reported that its infrastructure is fully functional but that people may experience delays.
"There has been no physical damage to our network," a T-Mobile representative said. "Users can potentially expect congestion, and it may take a while to connect." The representative added that phone calls will also be prioritized.
Rumors that mobile networks had been shut down to prevent terrorists from using cell phones to detonate bombs appear to have been quashed for the present.
O2's representative said: "The government certainly hasn't asked us to put any restrictions on network usage, but we will continue to monitor the situation."
Jo Best of Silicon.com reported from London.