Most patients still need to make at least two telephone calls to contact NHS Direct, and then wait to be called back by a nurse, health analysts say.
Most patients have to make more than one call
The government's original vision for the service was immediate care at the end of the phone.
A University of Southampton team looked at calls handled by NHS Direct for 31 English GP Cooperatives.
Only nine (29%) achieved single call access for all patients, their study in the British Medical Journal found.
Although 21 (68%) successfully integrated their out of hours calls with the NHS Direct service during the study period.
Calls to emergency ambulance services increased after integration, but the study authors said this might have been due to patients dialling 999 rather than waiting for a return telephone call.
A programme was set up to help GP surgeries integrate services with NHS Direct after a government review of out of hours care in England in 2000.
The review recommended that patients calling their GP surgery outside of working hours should be automatically diverted to NHS Direct for an initial telephone assessment.
Two call situation
Lead researcher Dr Val Lattimer said: "These results suggest that there are limited efficiencies to be gained from routing all incoming calls through NHS Direct if the workload of general practice providers is insufficiently reduced.
"At the heart of the model is that patients make a single call to access out of hours care - they call their surgery number and are diverted to NHS Direct.
"But for most people its a two call situation. They call their GP surgery number and get an answer phone message to call another number for NHS Direct or a cooperative.
"If you are very worried about a situation it is hard enough to find a pen and pad and write a number down, particularly in the evening or the middle of the night, but to make two calls is something we want to overcome."
She said she was sure the situation would improve, particularly as primary care trusts now have the responsibility for commissioning services locally.
This means PCTs can look to private companies to handle their calls if they think it will be more efficient.
A spokeswoman for the Department of Health said: "This report does not reflect the current picture of how out-of-hours services are performing.
"New arrangements are providing improvements to local out-of-hours services for patients. Patients are guaranteed a face-to-face consultation with a GP if needed and all out-of-hours services must now be delivered to national quality requirements."