Method for a radio telephone to search for higher priority networks

1. A method for a radiotelephone to search for higher priority public land mobile networks comprising:

camping the radiotelephone on a cell of a visited public land mobile network and registering on the visited public land mobile network;

uniquely identifying the cell;

searching for public land mobile networks with a higher priority than the visited public land mobile network while registered on the visited public land mobile network and camped on the uniquely identified cell;

storing a history of those frequencies found during the searching step, while camped on the uniquely identified cell, that are not of a higher priority public land mobile network, the history being associated with the uniquely identified cell;

periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone; and

if a history already exists for the uniquely identified cell, then updating the history with any new frequencies found that are not of a higher priority public land mobile network to any previously found frequencies in the history.

2. The method of claim 1 , further comprising:

scanning for higher priority public land mobile networks in frequencies other than those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped while it is registered.

3. The method of claim 1 , wherein the storing step includes storing public land mobile network identifiers(PLMN IDs) associated with each absolute radio frequency channel number(ARFCN), that was found to be not a home or higher priority PLMN, in the seaching step.

4. The method of claim 1 , wherein the storing step includes storing an individual history of those frequencies found that are not of a higher priority public land mobile network for each of a plurality of cells of the visited public land mobile network.

5. The method of claim 1 , wherein the storing step includes adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history.

6. The method of claim 1 , wherein the history in the storing step is started anew at least one of the group of: each time the radiotelephone is power on and after a timeout period.

7. The method of claim 1 , further comprising:

giving a list of public land mobile networks to the radiotelephone; and

erasing the history if there is a change in a stored preferred public land mobile network list.

8. A method for a radiotelephone to search for higher priority public land mobile networks comprising:

camping the radiotelephone on a cell of a visited public land mobile network and registering on the visited public land mobile network;

giving a list of public land mobile networks to the radiotelephone;

uniquely identifying the cell;

searching for public land mobile networks with a higher priority than the visited public land mobile network while registered on the visited public land mobile network and camped on the uniquely identified cell;

storing a history of those frequencies found while camped on the uniquely identified cell that are not of a higher priority public land mobile network for each of a plurality of cells of the visited public land mobile network, the history being associated with each uniquely identified cell;

periodically scanning for higher priority public land mobile networks except in those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped while it is registered;

periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone;

if a history already exists for the uniquely identified cell, then updating the history with any new frequencies found that are not of a higher priority public mobile network to any previously found frequencies in the history.

9. The method of claim 8 , wherein the storing step includes storing public land mobile network identifiers(PLMN IDs) associated with each absolute radio frequency channel number(ARFCN) that was found to be not a home or higher priority PLMN, in the searching step.

10. The method of claim 8 , wherein after the scanning step further comprising:

adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history.

11. The method of claim 8 , wherein the history in the storing step is started anew at least one of the group of: each time the radiotelephone is powered on and after a timeout period.

12. The method of claim 8 , further comprising:

erasing the history when there is a change in a stored preferred public land mobile network list.

13. The method of claim 8 , wherein the storing step includes storing the history in one or more of a non-volatile memory of the radiotelephone and a subscriber identity module associated with the radiotelephone.

14. A method for a radiotelephone to search for higher priority public land mobile networks comprising:

camping the radiotelephone on a cell of a visited public land mobile network and registering on the visited public land mobile network;

giving a list of public land mobile networks to the radiotelephone;

uniquely identifying the cell;

searching for public land mobile networks with a higher priority than the visited public land mobile network while registered on the visited public land mobile network and camped on the uniquely identified cell;

storing an individual history of those frequencies found during the searching step while camped on the uniquely identified cell that are not of a higher priority public land mobile network for each of a plurality of uniquely identified cells of the visited public land mobile network;

periodically scanning for higher priority public land mobile networks except in those frequencies listed in the history for the uniquely identified cell in which the radiotelephone is camped while it is registered; and

periodically searching, at a slow rate so as not to consume much battery power, for higher priority public land mobile networks in all radio access technologies and frequencies supported by the radiotelephone;

if a history already exists for the uniquely identified cell, then adding any newly found frequencies that are not of a higher priority public land mobile network to any previously found frequencies of the history to update the history previously found frequencies with any new frequencies found that are not of a higher priority public land mobile network.

15. The method of claim 14 , wherein the history in the storing step is started anew at least one of the group of: each time the radiotelephone is powered on and after a timeout period.

16. The method of claim 14 , further comprising:

erasing the history when there is a change in a stored preferred public land mobile network list.

17. The method of claim 14 , wherein the storing step includes storing public land mobile network identifiers (PLMN IDs) associated with each absolute radio frequency channel number (ARFCN) that was found to be not a home or higher priority PLMN, in the searching step.