Currently there are a number of frame rates. In the PAL world (which is by far the largest TV audience) the frame rate is 25 and only 25fps.
The NTSC world seems to thrive on having five frame rates – 23.976, 24, 29.97, 30 and 59.94. Conversion within those rates is fairly simple maths, but a right royal pain. The real pain though is going to 25 frames without hybrid fields or speeding up a program by 4.1% or slowing it by nearly 20%.
Best hope, if maintaining speed is required, is hardware conversion. The introduction of HD didn’t change anything because SD is concurrent and historic frame rates like 24 are still required. If anything HD has introduced more variables and complicated life.