According to the UK Band plan the only difference between FM simplex and C4FM/DV simplex channels, are the Calling Frequencies... FM calling on 2m is generally agreed to be 145.500 Mhz on C4FM its 144.6125 Mhz on FM 70cm Calling is on 433.500 Mhz on C4FM its 438.6125 Mhz......because nothing else has been agreed the rest of the 2m and 70cm bands are general classed as all mode so should you make a C4FM contact on 144.6125 you can move to 145.525 or 145.475 so long as you've checked the frequency is not in use in FM first.....Here in my Area we as Digital C4FM users tend to stay in the band area of 144.6375Mhz to 144.7875 Mhz avoiding of course the usual RAYNET frequencies...
144.500-144.794MHz All Modes*
This area of the 144MHz band is allocated to any mode with a maximum bandwidth of 20kHz. Here you can find a mixture of telephony and other modes that can include data, digital voice calling and image modes (Slow-scan TV, Fax etc). The use of amplitude modulation (AM) is also acceptable within the All Modes segment but users are asked to consider adjacent channel activity when selecting operating frequencies. A number of AM users are now using 144.550MHz for their telephony contacts.
144.794-144.990MHz Machine Generated Modes (MGM)
Machine generated modes with a maximum allocated bandwidth of 12 kHz will be found within this sub-band. The modes, some of which can be unattended, include Automatic Packet Reporting System (APRS), Digital Voice Gateways and AX25 (packet) data systems.
144.9900-145.1935MHz Repeater Input Channels (FM/DV)
There are 16 common repeater channels allocated throughout IARU Region-1 all using a 12.5kHz channel spacing system. The input channels commence at RV48 (145.0000MHz) continuing through to RV63 (145.1875MHz).
145.2000-145.5935MHz Simplex Channels (FM/DV)
Nestled between the repeater input and output frequencies are around thirty simplex channels. These all adopt a 12.5kHz spacing regime and are designated V16 (145.200MHz) through to V48 (145.5935MHz). Here you will find both fixed station and mobile activity especially around the mobile calling channel on 145.500MHz.
145.5935-145.7935MHz Repeater Output Channels (FM/DV)
The 16 repeater output frequencies are located 600 kHz higher than the input frequencies and this is commonly known as the repeater ‘shift’. The output channels commence at RV48 (145.6000MHz) continuing through to RV63 (145.7875MHz). Until recently all voice repeaters used frequency modulation (FM) but this is slowly being superseded by digital voice (DV) communication. Therefore you are likely to find a mixture of FM and DV throughout the repeater network.
433.394 – 433.600MHz Simplex Channels (FM/DV)
This area of the band is allocated to simplex channels U272 to U288 that may either be used for FM or digital voice (DV) communication. The FM calling channel is on U280 (433.500MHz) and operators using AFSK radio-teletype may find activity on U288 (433.600MHz).
146 – 147 MHz Simplex Channels (DV/DATA) full licence and NoV required
Ofcom’s objective in allocating this new part of the spectrum was to encourage amateurs to experiment and test new communications schemes and systems rather than provide for “more of the same”. In terms of band planning, therefore, with the exception for a small slice at the top of the 146-147MHz band (~100KHz for digital voice; D-Star, DMR etc.) we currently intend to leave the majority of the new allocation open for experimentation with ‘moderate’ (up to 500 KHz bandwidth) experimental digital voice and data transmissions.