FSK signal in matlab Phase problem

[gresoul]

hello Im trying to generate a FSK signal in Matlab. The FSK signal is the concatenation of sinusoidal tones at two differend frequencies 1650 Hz and 1850 Hz

when the following code is run in matlab the first sinusoid does not smoothly trasition into the the second sinusoid (in the middle of the signal):

fs = 15000;
tn = 0:1/fs:0.05;
phi2 = 0;
xx = [cos(2*pi*1650*tn), cos(2*pi*1850*tn + phi2)];
plot (xx);

a different value for phi2 (the second sinusoid) is needed for the signal to look smoother. what is the best value for this phase?

Thanks