Can i use 4.0 MHZ crystal oscillator instead of 3.5795MHZ for making DTMF decoder?
Assuming that you are using a DTMF chip (there is no information in your question) then the chip will use timing derived from the crystal oscillator to operate the switched capacitor filters in the chip. For example, the MT8870D datasheet says:


  Separation of the low-group and high group tones is achieved by applying the DTMF signal to the inputs of two
  sixth-order switched capacitor bandpass filters, the bandwidths of which correspond to the low and high group
  frequencies. The filter section also incorporates notches at 350 and 440 Hz for exceptional dial tone rejection (see
  Figure 3). Each filter output is followed by a single order switched capacitor filter section which smooths the signals
  prior to limiting. Limiting is performed by high-gain comparators which are provided with hysteresis to prevent
  detection of unwanted low-level signals. The outputs of the comparators provide full rail logic swings at the
  frequencies of the incoming DTMF signals. [Emphasis mine.]


In addition, page 10 shows one frequency for the crystal / clock with no deviation!




  Will it have any problem using the 4.0 MHZ instead of the 3.5795 one?


It certainly will. The passbands of the filters will be out by \$ \frac {4.0}{3.5795} \$. Time to order the right crystal.