Mobile Number Portability,a service that allows a user to swith operators while retaining the number,is likely to be delayed as state-run MTNL has expressed inability to implement it before the next year due to technical constraints. We will not be able to implement MNP before December 31,2009,due to a technical problem. We are looking at implementing it by March 31,2010, MTNL CMD R S P Sinha said.