  Pulsed gamma-ray emission from millisecond pulsars (MSPs) has been detected
by the sensitive Fermi, which sheds light on studies of the emission region and
mechanism. In particular, the specific patterns of radio and gamma-ray emission
from PSR J0101-6422 challenge the popular pulsar models, e.g. outer gap and
two-pole caustic (TPC) models. Using the three dimension (3D) annular gap
model, we have jointly simulated radio and gamma-ray light curves for three
representative MSPs (PSR J0034-0534, PSR J0101-6422 and PSR J0437-4715) with
distinct radio phase lags and present the best simulated results for these
MSPs, particularly for PSR J0101-6422 with complex radio and gamma-ray pulse
profiles and for PSR J0437-4715 with a radio interpulse. It is found that both
the gamma-ray and radio emission originate from the annular gap region located
in only one magnetic pole, and the radio emission region is not primarily lower
than the gamma-ray region in most cases. In addition, the annular gap model
with a small magnetic inclination angle instead of "orthogonal rotator" can
account for MSPs' radio interpulse with a large phase separation from the main
pulse. The annular gap model is a self-consistent model not only for young
pulsars but also MSPs, and multi-wavelength light curves can be fundamentally
explained by this model.
