Yes, I find Voipcheap are reliable and call quality seems good. They charge around 3p per minute for calls to UK mobiles compared with around 10p per minute using sipgate.
Voipcheap do not require registration, so you do not need to use an spX for them Instead use a Voice Gateway. Bit of a learning curve – start here:
http://www.obitalk.com/forum/index.php?topic=526.msg3124#msg3124I don't know how you wish to use your OBi – do you have a PSTN line etc? I'm assuming that you live in the UK and that sipgate is on sp1. Here's a suggested config with Voipcheap added as Voice Gateway 3. It may need some fine tuning:
Physical Interfaces > PHONE Port > PrimaryLine: SP1 Service
Voice Service > Auto Attendant > PrimaryLine: SP1 Service
Physical Interfaces > PHONE Port > DigitMap:
([1-9]x?*(Mpli)|[1-9]S9|[1-9][0-9]S9|999|112|**0|***|#|**1(Msp1)|**2(Msp2)|**3(Mvg3)|**8(Mli)|**9(Mpp)|(Mpli))
Physical Interfaces > PHONE Port > OutboundCallRoute:
{([1-9]x?*(Mpli)):pp},{(<#:>|999|112):li},{**0:aa},{***:aa2},{(<**1:>(Msp1)):sp1},{(<**2:>(Msp2)):sp2},{(<**3:>(Mvg3)):vg3},{(<**8:>(Mli)):li},{(<**9:>(Mpp)):pp},{(Mpli):pli}
Service Providers > ITSP Profile A > General > DigitMap:
(<**3>07xxxxxxxxx|0[123]xxxxxxxxx|0[4568]xx.|1xxxx|1xxxxxx|00xx.)
Physical Interfaces > LINE Port > DigitMap:
([2-9]xxxxxxS0|0[1-9]xxxxxxxxxS0|xx.)
Voice Services > Gateways and Trunk Groups > Voice Gateway3 >
Name: voipcheap
Access Number: sp1(sip.voipcheap.co.uk)
DigitMap: (<0:0044>[123]xxxxxxxxx|<0:0044>7[1-9]xxxxxxxx|0044[1237]xxxxxxxxx|00xx.)
AuthUserID: set in voipcheap web site.
AuthPassword: set in voipcheap web site.
Using this config when you dial an eleven-digit number starting 07 (UK mobile phones), the call will automatically divert to vg3. The vg3 DigitMap will remove the leading "0" and replace it with "0044". This is the international format that voipcheap requires. This should all be seamless to the user who dials 07xxxxxxxxx from the OBi phone.
For once, I can say for sure that this works – it's how part of my own setup is configured