My broker,Global, will not accept any funds until your account is approved. Do not send funds to any broker, IB or otherwise, until you are approved. I know that IB requires you to indicate how you will be depositiing funds in order to complete their application. Just say check. Then, once approved, wire the funds, and cancel the check deposit.
I thought that would be the case, IB's list of application steps doesn't make this clear at all though.
I am just in same process. It looks to me that when you send scanned copies of required documents you are approved nearly immediately. You can wire funds. I asked on forum question about funding with transfer of US long stock but it seems nobody knows. This may be can the cheapest and quickest option.
A wire is the fastest way to fund an account. Transferring positions from another broker can take 4+ days. Details and time estimates are on the funds & banking page under the accounts tab.