If you're looking at radio waves then the mirror will have to be made of thicker metal, because as you increase the wavelength you also have to increase the thickness of the metal to get the same reflectivity. That's actually how satellite dishes work. They're basically a big curved mirror that concentrates all of the microwaves coming down from the satellite. They're often full of holes to keep the weight down, and this doesn't matter because the wavelength of the waves is larger than the holes. This is the same principle as seeing a light on in your microwave. You can see the light escaping through the door but the microwaves aren't escaping because they're too long. Once you get beyond visible light into the shorter wavelengths; ultraviolet light is easy to make mirrors for, but x-rays are very difficult. And so making x-ray telescopes is very difficult. Sometimes they do it by using a bag of gas to act like a lens rather than mirrors or by using a metal mirror but at a very grazing angle which makes the mirror very large. Mobile phone waves are at the microwave end of radio waves, and a sheet of aluminium would work nicely as a mirror for those.
Source : the naked scientists
One can see that for making lenses, materials of different refractive indices can be used based on required convergence, divervence and dimensions can be compared to those of the above described mirrors, Although there may a problem that making enormous lenses for radio waves require materials/machinery that we may not have at the moment, mirror though as you see are the big satellite dishes that we have seen many times.
The earliest accurate determination of wavelength was, I think, by Michelson. Using his invention, the Michelson Interferometer, he could turn a micrometer dial and actually count how many wavelengths he moved a mirror. Reasonable monochromatic light could be had at the time from mercury vapor (or other elemental) discharge tubes or from a monochromator (a spectroscope with a slit on the output to select a color). This was around 1880. I confess I don't know for sure. He was determined to measure the speed of light. Exactly when he worked on wavelength I don't know. I'm sure someone here can add that info.
http://physical-optics.blogspot.com/2011/06/michelsons-interferometer.html
Michelson was able to count a lot of wavelengths so that the mirror moved enough to get a good average from the mechanical measurement. He was able to measure the wavelength of precisely known colors so that the results were easily reproduced by others. At the time there was a lot of interest in the spectra of excited atoms of elements and of the sun and stars through the new medium of photography. Photographic spectra of a star was done first in 1863.
Once you have a wavelength and the speed, which Michelson also determined to a high degree of accuracy by refining the the rotating mirror method, the frequency is just f=velocity/wavelength. The frequencies are crazy big numbers like the red in a helium-neon laser is 4.7376 x 10^14 per second or 473.76 THz. That's tera-Hertz and it is nice that tera- is also trillion. This is why people use wavelength in nanometers, so that the red from the laser is described as 632.8nm, which is a lot easier. If you read older material you will see that we used a slightly more convenient measure, the Angstrom, which is 1/10 a nanometer. The same light is 6328 $\overset{\circ}{A} $. The Angstrom is abbreviated as a capital 'A' with a little dot or circle over it. (It is in the UTF8 character set but I'm not sure will render for everyone, so I faked it in LaTeX.)
I think I got that frequency calculation right. By the way, it is accepted to use a Greek lambda $\lambda $ for wavelength and nu $\nu $ for frequency. Then $velocity\; =\; \lambda \nu $.
Best Answer
There is no theoretical physical limit on the wavelength, though there are some practical limits on the generation of very long wavelengths and their detection.
To generate a long wavelength requires an aerial of roughly one wavelength in size. The accelerated expansion of the universe due to dark energy means the size of the observable universe is tending to a constant, and that will presumably make it hard to generate any wavelengths longer than this size.
As for detection, we tend to measure the change in the electric field associated with an EM wave not its absolute value. As frequencies get lower we will need either increased intensity waves or ever more sensitive equipment. Both of these have practical limits, though I hesitate to speculate what they are.